Ask HN: What does it mean to iterate when building a startup?

YC and other accelerators often talk about "iterating" when it comes to the early stages of a startup, but to paraphrase Inigo Montoya, people keep using this word but I do not think it means what they think it means.

Sometimes this seems to refer to pivoting to a totally new business idea, sometimes it seems to just mean talking to a different set of customers, other times it seems to be a way of saying that a new feature was shipped.

Is there a generally accepted definition of what it means to iterate, and when you should do it?