ICO's are just abbreviation for the term "Initial Coin Offering" It means that someone offers investors some units of a new cryptocurrency or crypto-token in exchange against cryptocurrencies like Bitcoin or Ethereum. (c)blockgeeks

Are they scam?

No they're not, but most of them are scams. ICO's are just new projects which uses cryptocurrency to run let say a messenger project that requires token in order to send message as a load. (That's the simplest way i can explain it) But it depends on the project some of the ICO's uses token as utility and some are for security.

To avoid scams it's better to do a background check of the project, members and other informations. This thread that I've made might help you feel free to check: https://bitcointalk.org/index.php?topic=3196383.msg33152916#msg33152916