A mix featuring songs that have been carefully choosen, mixed and recorded onto an analog or digital medium. The name 'mixtape' is used because they were originally mixed and recorded onto cassette tapes by DJs in the 70's 80's and 90's. Mixtape still prevails over the term Mix-CD as the main word used to describe DJ mixes of this nature.
Romantics call compilations they put together for loved ones 'mixtapes' because it is more romantic than 'compilation albums'. Usually when giving "Ballad Mixtapes" to loved ones, there is a thought process on the selection of songs and the arrangement of the playlist. .
To make it simple, mixtapes should be mixed, everything else in reality is just a compilation.