This is in distinction from two-track stereo recorders where the two tracks cannot be recorded or played back independently. Multitrack recorders are designed to be used in combination with a mixer.
A decent 8-channel mixer without an audio interface built-in can easily set you back $/£200, and once you add multi-track recording via USB into the equation you can easily hit the $/£500 mark.
These require an audio interface or mixer, which gives you more control over your recording ... but if you plan to get into multitrack audio mixing eventually, you want a pair that are ...