Drawdown
A drawdown is the decline from a peak in a running results total to the lowest point that follows it.
In plain English
It describes the worst stretch rather than the average one, which is the part people actually have to live through. A profitable record can still contain a long and uncomfortable drawdown.
Example
A total peaks at plus 12 units, falls to minus 3, then recovers. The drawdown was 15 units.
Why it matters
Drawdown, not average return, is usually what causes people to abandon a process at the worst moment.