Explanation of Error related to memory

Hi all,
I am learning GPU programming and wanted to know what maximum grid size my machine can resolve so I went for a 1000x1000x500 grid and I got this error. Can you please explain what it is saying in easy words

ERROR: Out of GPU memory trying to allocate 7.451 GiB
Effective GPU memory usage: 97.26% (30.877 GiB/31.749 GiB)
CUDA allocator usage: 30.531 GiB
binned usage: 30.531 GiB (30.531 GiB allocated, 0 bytes cached)