By now most people, even those vaguely tuned into finances, have heard the phrase "meme stock." But if you're just catching up, here are some basics.

The market saw a fresh meme stock frenzy this week. While high exuberance can be a contrarian sell signal, sources say the market is still in good shape.

Financial markets once again have been seized by meme-stock mania. In mid-July, a frenzied rally erupted around a cohort of beaten-down companies, including Opendoor Technologies Inc., Kohl’s Corp. and Krispy Kreme Inc.