Housecarl

There are two categories of housecarl in The Elder Scrolls V: Skyrim: those who serve the Dragonborn at one of his/her homes, and those who serve the Jarls of the holds.

Dragonborn's housecarls
All the Dragonborn's housecarls are potential marriage candidates as well as followers.

Jarls' housecarls
A Jarl's housecarl acts as their personal bodyguard and rarely leaves their side.

Huscarl