According to leading baby name website babycenter.com, Boo could mean beautiful and is of French origin, but is not currently a common name in the UK.
Walt - meaning army ruler - is a more traditional name, a derivative of the German-based Walter. According to babynames.co.uk, it is ranked as the 429th most popular name at the moment.
Here are some of the more unusual names famous types have chosen for their offspring:
- Sir Rumi and Carter - Beyonce and Jay Z
Beyonce and Jay Z revealed the names of their twins in July 2017.
The rapper later explained that Rumi is the name of their favourite poet, a 13th Century Persian wordsmith, and that Sir was named so because of his overall attitude.
He said: "Sir was like, man, come out the gate. He carries himself like that. He just came out, like, Sir."
The 2017 ONS figures show six boys and six girls were named Rumi. The name Carter was popular for boys, with the ONS list showing 1,025 boys named Carter last yer, while only five girls were were also given the name.
- Bear - Take That's Howard Donald, as well as Cheryl and Liam Payne
Singer Donald named his second child Dougie Bear and a few months later Cheryl and Liam Payne appeared to follow in the same footsteps by picking Bear as the name for their baby boy.
Payne later explained that the name for his child was down to the noises he made as a new-born.
He told James Corden on The Late Late Show: "When he was born, one of the midwives said it, he had this thing where if they don't have a good cry they get fluid in the lungs which is quite serious.
"He was going like, 'Grrr, grrr,' when he was sleeping. So I had specialists running in and out of hospital all day, my missus was asleep, I had like 10 doctors come into the room. And in the end, the guy was just like, 'I'm not being funny, there's nothing wrong with him, he just likes to make a lot of noise.'
"And that's carried on ever since, so it just became Bear."
In 2017 the name was still being used outside of celebrity circles, with the ONS list showing 85 boys were called Bear.
- River Rocket, Buddy Bear Maurice, Poppy Honey Rosie, Daisy Boo Pamela and Petal Blossom Rainbow - Jamie and Jools Oliver
The Olivers have always opted for whimsical names for their children and the celebrity chef has said he leaves the choices all down to his wife, who has shown an affinity for florals.
The annual list from the ONS shows that 2,527 girls were named Poppy last year, while 2,040 were named Daisy. Only six girls were given the name Petal in 2017.
A total of 164 girls were named River, while 205 boys were also named as such. A total of 169 boys were named Buddy last year.
- Moxie CrimeFighter - Penn Jillette and Emily Zolten
Magician Jillette said he chose the name Moxie for his daughter because it represents "old fashioned spunk and energy".
He said the choice of CrimeFighter as a second name was more of a joke, telling People: "When she gets pulled over by the police she can show her licence and say, 'We're on the same side, officer. My middle name is CrimeFighter.'"
- Pilot Inspektor - Jason Lee and Beth Riesgraf
This baffling name is not even a real job, but the My Name Is Earl actor and his ex-fiance named their son after the Grandaddy song He's Simple, He's Dumb, He's the Pilot.
- Audio Science - Shannyn Sossamon and Dallas Clayton
The 40 Days and 40 Nights actress said she did not consult a name book when she was looking for ideas for her son. Instead, she said her boyfriend read through the dictionary.
- North - Kim Kardashian and Kayne West
The reality star and the rapper named their first child together after a point on the compass because they reportedly saw North as "the highest power" and regarded their daughter as their highest point together.
- True - Khloe Kardashian and Tristan Thompson
Reality TV star Khloe revealed True's name shortly after her birth in April. She posted on Instagram saying simply: "Baby True."
She later explained that she wanted her child to have the first name T, after her partner, and also that it was her great-grandfather's first name and her grandfather's middle name.
- Kal-El - Nicolas Cage and Alice Kim
Cage showed off just how much of a Superman fan he was when he chose the superhero's Kryptonian name for his son.
He told People: "I wanted a name that stood for something good, was unique and American and that's all three. I just thought it was a beautiful name and it had kind of a magical ring to it."
According to the ONS list, 19 boys were named Kal-El across the UK and Wales last year.
- Apple - Gwyneth Paltrow and Chris Martin
The actress and the Coldplay frontman looked to the fruit bowl to name their oldest child.
Paltrow told Oprah Winfrey: "(Apple) sounded so sweet and it conjured such a lovely picture for me. You know, apples are so sweet and they're wholesome and it's biblical and I just thought it sounded so lovely and ... clean! And I just thought, 'Perfect'."
- Moon Unit - Frank and Gail Zappa
Moon Unit was one of the first celebrity babies to bear the brunt of the fashion for unusual names.
Gail told The Times that Frank told her: "You can name it Moon or Motorhead." She added: "You know, you're not (truly) related to your partner in life until you have a child together. So we became a family unit and that's the significance of Moon's middle name."
- Heavenly Hiraani Tiger Lily - Michael Hutchence and Paula Yates
The TV star and the INXS singer reportedly chose the name for their child by giving everyone a say.
Apparently Pixie, one of Yates' daughters with Sir Bob Geldof, chose the name Heavenly, Hutchence chose Hiraani, and Yates chose Tiger Lily. She now goes by the name Tiger.
According to the ONS figures, last year seven girls were named Tigerlily, spelt as one word and not two, and 12 boys were named Tiger. More popular was the name Pixie, with 124 girls given the name in 2017.