Townhouse is a medium-density type of dwelling where property has separate entrance from the street and sometime even private back yard, but still has neighboring units on its sides (share at least one external wall with them). Townhouses are typically two or more floors up (even 5-storey townhomes are pretty common too).
It’s a house, but with neighbors living VERY closes to you.
By the type of ownership Townhouses are divided for Condo (condominium) and Freehold. Condominium townhomes are governed by Condo Association where owners have to obey their rules and restrictions and pay monthly maintenance fees to maintain the common areas (security, pool, insurance, lawn care and etc). Freehold townhomes are more like single family homes. The owners are free from any condo rules and fees, but have to take care of the property on their own.
Owning a typical condominium unit means owning an air space surrounded by the walls, whereas each exterior element is held by the community. A very important detail about the townhouse is that the homeowner buys the rights on the particular parcel of land on which the housing is built.