A bubble is when everyone is talking about cryptos, e.g. your taxi driver, the bellboy, etc. Outside of my close circle of tech colleagues zero people are talking about Bitcoin.
A bubble is when something's cost differs from its intrinsic value - a bubble can happen on something which is shockingly insignificant. Bitcoin's "intrinsic value" is extremely hard to define, so we could just call a bubble whenever the price rises extremely dramatically without much reason (such as now).
Of course every time there's a bubble a huge amount of people convince themselves that this is not a bubble and that it's the new norm - otherwise it wouldn't be a bubble.
Bitcoin has had several bubbles already, and this time it's got some friends getting a big slice of the action. I wouldn't say it's
quite a bubble for Bitcoin yet - it sure as hell is for a lot of pointless alts - but it's definitely on the verge of one and hovering around the point at which I'd call it a bubble.