It means they can play cds with mp3 songs recorded on them (as opposed to normal audio) , just like your computer can.
Thus a cd audio that can hold only 80 minutes normally can hold maybe 10 albumns + of songs recorded as mp3s
OnePlus 5T review: Hands-on
Illustrator Andrés Lozano on his improv line work, brazen use of colours & hand sketching
iPhone X review
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