A petty problem or issue is one that's annoyingly small and not very important.
When people talk about something being petty, they usually mean it's trivial, like someone complaining about a minor inconvenience or getting upset over a tiny thing. It's often used to describe behavior or reactions that are seen as unreasonable or overly sensitive. For example, if your friend gets mad at you for being five minutes late to meet up, and you think they're overreacting, you might say their concern is petty.
How common is "petty"?
Word petty is considered uncommon in modern English. It has a balanced usage among all categories: speech, fiction, newspapers and academic texts.
Definitions
adjective
Having little or no importance.
Example: a petty fault petty squabbles
Of persons or their behaviour: marked by or reflective of undesirably limited interests, sympathies, or views; begrudging, selfish, small-minded; also, preoccupied with subjects having little or no importance and not mindful of broader concerns.
Example: Such literature may well be anathema to those who are too docile and petty for their own good.
Inclined to cause frustration or annoyance to others out of spite over minor grievances; extremely vindictive.
Example: My cousin is so petty—I forgot his birthday and he's been making snarky comments all week.
(historical) Of or relating to the lowest grade or level of school; junior, primary.
Little or small in size.
Secondary in importance or rank; minor, subordinate.