Open-limping means being the first to enter the pot by just calling the big blind, instead of raising or folding.
How it's calculated
The healthy ranges on the side are guidelines for NL Hold'em cash games with 100 bb stacks, the same ones Flopmortem compares your game against. Use them to spot big deviations, not as an exact target: they depend on the table, your opponents and your style.
How to read your Open-limp
In cash games, entering first with a limp is almost always a mistake: you give up winning the pot right away, invite the blinds to see a cheap flop and announce a mediocre hand. The healthy play is to raise or fold.
Don't confuse it with limping behind other limpers (over-limping), which makes a bit more sense with speculative hands. Flopmortem only counts open-limps.
If your Open-limp is out of range
Too high
You open-limp often. Raising or folding is almost always better.
How many hands you need to trust it
Flopmortem doesn't flag your Open-limp as a leak until it has at least 40 opportunities. From there it calculates it with its 95% confidence interval: if the whole interval falls outside the healthy range, the leak is confirmed; if only the measured value is outside, it's a trend. The guide how many hands you need to trust your stats explains it.