Very huge difference.
Bitcoin is the
Real BTCitcoin (BTC) while
Bitcoin cash (BCH)is a hard fork of Bitcoin. It's a shitcoin whose greedy and scam owners created to rival
BTCitcoin and to confuse newbies into believing that it's the real bitcoin, yet it isn't. It's just another altcoin and a bitcoin copycat.
Do not be tricked into buying it thinking it's BTC