Skew compares the implied volatility of out-of-the-money puts against equivalent calls. The convention is a 25-delta comparison, and the resulting number says which tail the market is paying up for.
The equity baseline
In equity index options puts are almost always more expensive. Institutions hold equities and buy protection, so there is persistent structural demand for downside. That persistence is why equity skew is read as a level against its own history rather than against zero — skew being negative means nothing, since it is always negative.
Why crypto is different
Because the participant base is different, as set out in call-heavy books in crypto. There is no large base of holders who must own the asset and therefore must insure it, and the dominant expression is upside.
So crypto skew can and does sit positive for extended periods — calls richer than puts — particularly in strong trends. A trader importing the equity prior sees “calls bid over puts” and reads euphoria, when it may simply be this market’s ordinary condition for the regime it is in.
How to read it without a stable baseline
Against its own recent history, per coin, and with the sample size stated. That is the same discipline as funding extremes: an extreme is a claim about a distribution, and the distribution has to be this asset’s own.
Crypto makes that harder because the history is short and the regime changes. A coin with a few months of options history has no distribution worth quoting a percentile against, and saying so is more useful than producing an authoritative-looking number.
What it is actually good for
Direction of change rather than level. Skew moving sharply toward puts during a rally is a real signal that someone is paying up for protection while price rises — a disagreement between the tape and the options market. That is informative in any market, and it does not require knowing where the long-run baseline sits.