WMA is an acronym for Windows Media Audio and it is a file format that was developed by Microsoft and it deal mainly with audio data compression.
MP3 stands for MPEG-1 Audio Layer 3 and it is currently the most well-known audio format. This audio encoding type is based on a variation of lossy data compression.
Converting WMA audio tracks to MP3 files is mostly done because the latter are the most common audio storage types that can be played on all devices.
This type of conversion can be performed with dedicated software tools, and it is also supported by more complex multimedia converters.