Borehamwood is a town in South Hertfordshire, on the north-west edge of London. It is in the borough / constituency of Hertsmere (which used to be called South Hertfordshire) and has the Hertsmere borough offices.
It is very popular for people who work in London as the house prices are slightly lower than the astronomical prices within London, yet it has good road access (being near the A1, M1 and M25), and also good rail access (the Thameslink line, which, when it works, is fantastic).
In many ways, Borehamwood is considered part of London. It's within the M25, within the "6 zone system" for Travelcards on the trains, and has London phone numbers. On the other hand, it's in the Watford postal district (postcodes start with WD), and is outside what is officially London.
Traditionally, Borehamwood was very (class divide bit coming up) working class, with Elstree, on the other side of the railway lines, being more middle class. This is now less true as there are a number of newer housing developments in Borehamwood itself as well.
Borehamwood is also famous for containing two film and TV studios (and in the past a third). BBC has a large site, "BBC Elstree" (see how Elstree is the preferred name). This is most well known for making Eastenders, and in the past has also made Grange Hill and Top of the Pops. About half a mile from this site is "Elstree Film and TV studios" (again with the Elstree!), built on the site of the old "EMI Elstree" studios that were used to make many films through the 50's to the 80's, including Superman. The studios now are used for things like Who wants to be a Millionaire? and Big Brother.
Borehamwood also has all the other things you'd expect... a naff high street, an "open air mall" with DIY shops, Next, supermarkets etc, a council run (but recently rebuilt and therefore in good condition) gym and swimming pool, a cinema, bowling alley, Holmes Place... and all the other sort of stuff. There's also a few parks so there's a lot of green space.
And no English town would be complete without a local football team - Borehamwood FC (!) - who are non-league but fairly high up in non-league terms.
Borehamwood is estimated to have a population of about 30,000. I suspect this includes Elstree, as technically Elstree is part of Borehamwood.
Don't confuse Elstree (adjacent to Borehamwood) with Elstree Village. This is about a mile away, and is a very small village. I believe the name "Elstree", referring to the village, pre-dates Borehamwood, although nowdays, "Elstree" proper is seen as part of Borehamwood.
In short, it's a nice place to live!