Stamp duty dates back to the 17th century, when almost every form of legal documentation was taxed – from marriage certificates to cheques. To show that the tax was paid, each document received an official stamp, which explains how today's duty got its name.
While its purpose is still largely the same today, modern stamp duty land tax is only added onto property and land transactions over the value of £125,000, and only applies if you live in England, Wales or Northern Ireland. There is a similar Scottish counterpart too, but that's called Land and Buildings Transaction Tax (LBTT). It's essentially the same premise, but is only applied to purchases above £145,000.
Whether the property you're interested in is leasehold, freehold or shared ownership, it's likely that stamp duty will come up on your radar at some point. Even if you're buying the property outright without a mortgage, you're still liable for stamp duty, though if you've inherited the home, you'll pay inheritance tax instead.