What are 'Farm' Scores?

What does farming mean here in etterna? Is it similar to Osu where players farm/grind for pp scores?

Basically, yes.

Much with any difficulty rating system, MSD is not perfect. As a result some charts are overweighted in terms of MSD and become the target of MSD farming.

Likewise, ratefarming can be used to submit several scores on the same chart at slightly different speeds.

At least, thats the way I understand it