The most common and most likely answer to this crossword clue is the 7 plus 3 plus 3 letter word BRIDGES THE GAP
I've seen this crossword clue in Financial Times
B
R
I
D
G
E
S
T
H
E
G
A
P
Buddy explains!
The straight part
We know that "Provides filler for" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case provides filler for = bridges the gap.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.