adjective, derived from the term MILF from the movie American Pie. A MILF is a Mother I'd Like to Fuck; MILFtastic is a term to describe such a woman who is usually old enough to have a teenaged kid but hot enough that most guys don't care and would love bang her hard all night long doggie-style.
Man, look at the cans on that MILF! They're huge. I'd love to tittie-fuck her. And that ass if fine, she's all-round MILFtastic!