To add on top of what others have mentioned, "500多个" basically means five hundred and something piece of X. (Edit: Be careful that "多个" is not a word here, the correct way to separate the word would be "500多" + "个")
"500多" Literally means 500 (and) something, or five hundred (and) something, in this context
Some personal rant below
While this kind of usage has already become relatively common nowadays, I would like to advise against writing it out this way with Arabic numbers personally.
Writing the word out with Chinese numbers, like "五百多个" is ok and everybody would understand it directly and immediately, however, if you write "500多个", then it could be confusing to readers even if the reader is native in Chinese, especially at first sight, because all the zeroes have been spelled out in the form of Arabic number despite the "and something" part in the original sentence, and what's worse in Chinese compared to similar English usage is that there isn't even a word function like (and) is this kind of expression. Therefore, Reader might be tempted to think those Arabic numeral zeroes in the sentence might actually mean the round number before they actually read the sentence clearly. To avoid such a situation, it would probably be better to use Chinese numerals instead of Arabic numerals in this expression.