What does Shares/Diff number represent on pools found blocks

When the pool I am mining finds a block what does the "Shares/Diff" number represent?

This is a proxy for "did we get lucky or not".

The shares numerator is the total number of weighted shares sent by miners trying to find the block. When you mine, you're asked to solve an easier problem on that block template (and if you solve it with a large enough gap, you find the block). When you find one of those "subblocks", you submit it to the pool, which accumulates the difficulties of the submitted shares. When a block is eventually found, that accumulated number is roughly proportional to the number of hashes the pool's miners have expended trying to find the block. So the shares numerator is a proxy for the total work done by the pool's miners.

The Diff denominator is the block's difficulty, which is proportional to the estimated number of hashes needed to find the block.

So the fraction represents how easily this block was found. If less than 1, you were lucky (it took less shares to find the block than expected). If more than 1, you were not (it took more shares to find the block than expected).

When the pool I am mining finds a block what does the "Shares/Diff" number represent?

I would need the source to be 100% sure but with the context provided I believe that is a measure of (work done by pool miners/blocks difficulty).

Work (hashes generated) by the pools miners is proportional to the number of weighted shares generated by miners while finding pools sub-blocks. Difficulty is based on the current estimated number of hashes that will be required to find a block on the Monero network.

In other words Shares/Diff is a measure of luck. Over (long periods of) time the fraction should approach 100%

If the fraction is below 1 then you are lucky. If the fraction is above 1 you are unlucky.