For rock fans, “jam” generally has two meanings, neither of them necessarily attractive. It’s either a self-indulgent, just-for-fun musical hang that musicians have in their garage when nobody else is around, or a kind of music (and band) that bros and stoners love, featuring songs that go on for 45 minutes of aimless, shapeless wankery.

In jazz, though, a jam session is a bit of a different beast. It’s a hang, sure, but it’s also a creative workout. Everyone’s there to hone their craft: Older musicians go to keep their chops in fighting shape, bat around new ideas and interact with associates old and new; younger ones go to get much needed bandstand seasoning, learn the repertoire, work on form and technique and see what they can pick up from the veterans. The whole point is not to encourage self-indulgence, but to cultivate discipline.

It’s also an amazing thing to watch. Like any workout, it increases the participants’ energy flow, then feeds on that flow so the music just gets more intense and exciting as it goes on. (That’s why jam sessions are so often late-night occurrences: so musicians can release the energy they’ve built up in their gigs from earlier in the evening.)

D.C. has been building quite a jam-session scene recently. Not all of them have proved durable: HR-57, which hosted the city’s best-known jam session, is currently searching for a new home. The beloved U Street Jazz Jam recently fizzled out after trying out several locations. But there are still enough going on around town that you could see a jam session five nights a week—sometimes more than one in a night. And none charges a cover. Here’s our guide to D.C.’s best jazz jam sessions:

Tuesdays: A low-key jam at Takoma Station

Once one of the city’s most popular jazz venues, Takoma Station (in guess which neighborhood) now mostly hosts smooth jazz and go-go. But on Tuesday nights from 7 to 10 p.m., the venue hosts a low-key jazz jam. “Low-key,” that is, in the sense that there tend not to be many people in attendance on a Tuesday night (mainly neighborhood folks out to grab a burger and beer at the bar), and the musicians tend to be a small coterie of regulars, usually led by guitarist Glenn Wiser. Nevertheless, drop in to this dimly lit joint and it’ll be swinging.

Thursdays: An unofficial jam at Dukem

Dukem Jazz, the name that U Street’s Dukem Ethiopian Restaurant adopts on Thursday nights, isn’t advertised as a jam session per se. It’s a basic jazz gig, a small band playing two sets while customers eat, drink and groove, and it’s proven quite a successful format. But a tradition has arisen from the weekly performances: The second set, which starts at 10:30 p.m., brings in instrument-packing musicians and, as if spontaneously, a jam session develops. (Dukem Jazz promoter even advertises the evenings with the tag “second set turns into a jam.”)

Fridays: Late sessions at Twins Jazz

Naturally, the weekends are where the late-night stuff gets going. Twins Jazz, the U Street staple, is the newest outpost on the jam-session scene with its Late Session, which goes down on both Friday and Saturday nights. Like Dukem, Twins starts its programming with two sets (9 p.m. and 11 p.m.) by a headline act. When the second set wraps, usually ‘round midnight, a local musician or group—Twins tries to get a different booking each week—takes the bandstand, gets started on some standards, and invites all comers to sit in (or sit down and watch) until 2 a.m.

Saturdays: Early sessions at Columbia Station

There’s a lot of edge and energy moving in the late night jams, but you need not wait until late to catch one. Columbia Station, an Adams Morgan bar that’s also an underappreciated jazz venue, kicks off a Saturday jam session in the late afternoon at 4 p.m. Led by pianist Peter Edelman (and whoever he brings with him each week), it’s another one that attracts a small group of regulars, with other musicians drifting in and out irregularly. Sometimes there are long stretches where it’s nobody but the house band; in that case, they just keep it going like it was a regular club set.

Sunday: All the jam sessions you could ever want

Interestingly, Sunday is the busiest day for jazz jams. Columbia Station gets started at 4:30 on Sundays, but this time goes all the way to midnight—the District’s only seven-plus-hour jam session. At 5 p.m., over at Dupont Circle’s Black Fox Lounge, begins the city’s most unique session: The DC Jazz Singers’ Jam, a forum for sharpening vocal improvisations (a craft that’s far too little seen or heard, in D.C. or anywhere else), usually hosted by vocalist Sharón Clark. Then at 6:30 p.m., back in Adams Morgan, Dahlak Eritrean Restaurant hosts the D.C. Jazz Jam, a weekly three-hour session with rotating house trios and, most weeks, a special guest artist.

Photo by Flickr user Evonne used under a Creative Commons license.