Ok kiddo, so you know how when you play musical notes, you can make different sounds by playing them in different ways, like fast or slow or loud or soft? Well, sometimes when people play notes one after the other in a certain way it doesn't sound very good.
Consecutive fifths is a fancy way of saying that two musical notes are played one after the other and they are five notes apart from each other, but then these same two notes are played again in the same way right after.
It's like if you were to say "apple" and then "orange" and then say "apple" and "orange" again quickly after. It just doesn't sound as nice as saying "apple" and then "banana" and then "orange" instead.
So in music, when people play consecutive fifths it doesn't sound very good and it's something that musicians try to avoid so that the music sounds nicer.