Upvoting is like favoriting something, but a boost bumps something up so it’s more likely to appear on the trending section.

So upvote means “I like it” and boosting means “more people should see it,” from what I understand.

Basically it moves content up. Having a few boosts has the same power as a ton of upvotes. Works in comments too.

It's used as a way to move quality content and posts into people's views. I don't know if it affects visibility on Lemmy though.