Meaning of “slop” - Learner’s Dictionary

slop

verb uk us /slɒp/ (present participle slopping, past tense and past participle slopped)
slop (sth) about/around/into, etc

If liquid slops about, it moves around or over the edge of its container, and if you slop it about, you make it move around or over the edge of its container:

Her hand shook, making her tea slop into the saucer.

(Definition of “slop” from the Cambridge Learner’s Dictionary © Cambridge University Press)