Hi!
A run on sentence is any sentence which just can't really decide when to stop and it just has no end and just really wants to shove as many topics in there as possible without even using a full stop it's like so annoying and can get really difficult to read because you don't ever get to just take a second and have a breather yanno so yeah that's what a run on sentence is it's really just going on forever and ever and never shutting up which can be pretty difficult to digest so maybe you understand what it maybe is now right because this entire answer has kind of been a run on sentence like jeez man wow okay hopefully this helps! =)