It means . . . NOTHING!
The measurements are averages, and vary from person to person and pregnancy to pregnancy and week to week. Basically, if you stop getting bigger at some point, that can be (but isn't necessarily) an indicator of a problem. Babies, in utero as out, grow in spurts sometimes, so it might easily mean your baby - or your uterus - had a growth spurt. Or is hanging out up high. Or you were especially well hydrated that day.
I believe measuring significantly ahead (like 5 - 6 weeks) might trigger some further investigation by an OB or MW, but one week off - or 3 like Kim - is not much to get too excited about. I'm interested to see what I'll measure end of this week - I was measuring 27 at 24 weeks, but suspect I'll be right on again this time at 29/30 weeks.