That's the second level for a "Senior" developer. The senior level band starts at 63. Below that are 59 (college graduate) to 62, which are the bands of Software Engineer and Software Engineer II. Above it are Principle (65-67) and Partner levels.
I was expecting the levels to be factors of 2. :(
Presumably an internal pay-scale ranking system. Government jobs, for instance, are ranked in a G(1?) - G12+ scale. Sounds a little goofy, but large enterprises need some method to standardize and track compensation.
Most college hires enter at level 59 (SDE/PM/SDET I)
Once you hit level 61, you're an II
Once you hit level 63 (maybe 64?), you're Senior
After Senior, it goes Principal then Partner.
why start at 59?
Without knowing, I would guess that lower numbers are used for non-developer employees (i.e. sales or marketing).
HR silliness. Supposedly, people are less pissed off by a ladder that puts them at 59 out of 70 than by one that puts them at 1 out of 12.
I've heard it was to avoid ambiguity with numbers used in an earlier system.