SLP (Simple Ledger Protocol) tokens are tokens built on the Bitcoin Cash blockchain, similar to ERC-20 tokens on Ethereum or SEP-20 tokens on SmartBCH.
They use OP_RETURN opcodes to store the data, since Bitcoin Cash does not have a native way to create tokens. There are discussions to create native tokens on Bitcoin Cash, like "group tokenization"  and PMv3 
These tokens are not miner-vlaidated and therefore it's possible to accidentally burn them. If you load your private key to non-SLP compatible wallet, your tokens will seem like dust to the wallet (546 satoshis) and will will send them as BCH, effectively burning SLP tokens.
Wallets that support SLP:
- Electron Cash SLP version - bitcoin.com wallet