A bitcoin bubble occurs when the sentiment around bitcoin is too positive and drives everyone to buy it. This then pushes prices into a bull market before sentiment changes and the bubble bursts, causing a sharp drop in prices known as a correction and potentially leading to a bear market.
You will hear many nocoiners and people spouting FUD on Bitcoin’s fiat price and comparisons to “tulip mania” will be more and more present during a bubble. Conversely, many moonboys will repeat the opposite sentiment, so be aware of both sides!
There are of course market cycles that occur and these tend to occur around the Bitcoin halving, but as you learn more about Bitcoin and how it works you will be able to make up your own mind about what you want to read in the “Bitcoin bubble”.