A laptop is a portable personal computer. A laptop has most of the typical components of a desktop computer but in a smaller case. The screen and keyboard are usually built in, and the desktop mouse is usually replaced by a trackpad.
Most laptops have a battery to provide power and a wireless card for internet access in remote situations.
Ubuntu can be installed on most laptops without issue, but it is not uncommon to require extra work to get a wireless card or trackpad working properly.