Yes, that's a good way to explain it. When we're watching from visit to visit, we're looking at the trend in percentile over time.50th percentile would be exactly average, 90% percentile means in a room of 100 kids his age hes heavier than 90 of them.
The only time percentiles posed a problem for my kiddos was when they were used to detect a head growth problem in one of my kiddos  extra imaging was requested and there was an actual reason for the extreme jump off of the datum points off of the growth curve.Would it be fair to suggest that growth curves and percentiles are used to detect changes in growth?