i see a lot of posts that mention growth spurts & particularly in regards to the 6-8 week mark in NBs & i was wondering what they involve?

DS had just dropped 1-2 feeds a day to 9 or 10 a day but has gone back to 11 a day in the last couple of days & i'm wondering if this is maybe a growth spurt or whether it's just 'normal' for babies to change the number of feeds per day (although i know 11 feeds is perfectly normal for his age)? also, DS has put on 1.5kg in the last 4 weeks & grown about 1.5cms so i'm wondering whether a growth spurt is something other than weight/height? is it developmental at this age as well?