TF slash, short and simple, is the love between too male bots...mecha yaoi. It can be sensual or quite sexual. Either way, it CAN and WILL happen. It's becoming popular no thanks to the new movie, but you'll find hot, steamy fanfiction/fanart from any series if you really need it. Just Google it. It's every where. Optimus loving innocent Bumblebee, Starscream seducing the mecha tyrant Megatron, Jazz being double teamed by Sunstreaker and Sideswipe...it's everywhere. Oh and be warned, it's pretty damn hot and addictive. You might catch the TF slash fever.
"Omg! Optimus and Megatron are THE hottest TF slash pairing EVER!"
" Psh! Yeah well we ALL know Megatron loves his little mecha-slut Starscream even more."