One definition of a sexual activity is any behavior that someone engages in alone, or consensually engages in with others, that is considered sexual by the people engaging in it. Sex researchers tend to survey people every few years, asking them what they think sex is, and then reporting back with "shocking" information that such and such group no longer considers X activity to be "sex". Of course any generalized definition of sex will fail. What is sexual changes over time, and is influenced by culture, gender, class, ethnicity, and more.
Having an open mind about what might be a fun and satisfying sexual activity may be good. But if you're not sure where to start, and you're like many of us who are under the impression that sexual activities are limited to something called foreplay and something else called intercourse, a list can be a helpful place to start.
Because we all have different body parts, and because even the Internet can run out of room, I've collapsed some of the activities into groups. Just fill in the body parts that you have that you want to use in sex, and away you go.
Don't forget that each of these activities may be given and/or received. And remember that none of these activities is called sex if it isn't consensual. If someone is forcing someone else to do any of these things, we call that sexual assault or rape. Sexual activities are reserved for those things we want to do.
Kissing: lips on lips, with and without tongue.
Kissing another other body part or having another body part kissed.
Giving or getting hickeys (using your teeth and mouth to leave temporary marks on a partners body).
Oral sex: using your mouth to stimulate a partner's genitals (cunnilingus, fellatio, analingus).
Using another body part (hands, elbows, feet, whatever works) to stimulate a partners genitals (penis and scrotum, vulva, vagina, and clitoris, anus and rectum).
Non-genital sexual touch: using another body part (hands, elbows, feet, whatever works) to erotically touch or explore your own or your partner's whole body.
Massage: using any part of your body to sensually touch and relax any part of your own or a partner's body.
Dry humping, fully clothed rubbing of your body with someone else's body (frottage).
Naked body rubbing, rubbing genitals together without penetration(tribadism).
Chest, breast, and/or nipple stimulation.
Masturbation: stimulating yourself for sexual pleasure.
Mutual masturbation: stimulating yourself with one or more person present.
Ejaculating during sex.
Sex toys: using alone or with a partner.
Restricting your own or a partner's movement during sex (tying up, restraining body parts).
Restricting your own or a partner's senses during sex (wearing headphones, blindfold, covering parts of the body so they can't be touched).
Pinching, spanking, or slapping for sexual pleasure.
Vaginal intercourse: using a penis or strap on.
Anal intercourse (using a penis or strap-on).
Dressing up during sex.
Doing a strip tease for yourself or a partner.
Having sex in the water.
Using food during sex play.
Talking dirty to each other.
Taking pictures, audio, or video during sex by yourself or with a partner.
Having sex in public or in semi-public spaces.
Doing role play of sexual fantasies.
Any sexual activity with multiple partners.
Having sex with a partner or by yourself while other people watch.