“Underground hip-hop” is a bit hard to pin down. Is it defined by rebellious philosophies, off-kilter backbeats, or just a shoestring budget without big corporate daddies? Whatever it is, it’s on “The Craft,” the third album by spunky San Francisco Bay Area duo Blackalicious. Their refreshingly rough, raw yet sugary-sweet beats lack the over-crisp sheen of radio-bound hip-hop, and their socially-conscious lyrics aren’t exactly school-dance sing-alongs. Nevertheless, “The Craft” is saturated with a creativity and defiant energy that you’d be hard-pressed to find elsewhere, least of all a platinum-seller.

Instead, Blackalicious concocts a funky hybrid of party-worthy diversions (like the Black Eyed Peas at their best) with Jurassic 5 lyrical wordplay, though the mix is effortless and fresh. Oversized MC Gift of Gab — who resembles a bespectacled Biggy — could match that classic rapper for tongue-twisting lyrical volume that’s clean as a whistle. (“Rhythm Sticks,” for example, is his second installment of the alphabet at warp-speed.)

It’s also a pleasure to hear that Gab has the social acuity to describe women as more than just an assortment of inflated body parts. On “Powers,” a sunny, electric guitar-driven anthem, his cheeky exultations of sex come in more imaginative flavors than a thousand 50 Cents could muster: “She’s so fly/ Lethal injection/ Frozen in my step like deep in a breath/ Keepin’ a brethren like me in a head spin/ Doc take a rain check/ She is the medicine.”

Aside from his inspired lyricism — and incomparably subtle touch for rhyme — Gift of Gab has an unparalleled grasp on the technicalities of rapping. He has almost impossible timing on “My Pen and Pad,” landing every well-enunciated syllable square on the bass down stroke. Despite its title, the track is an ode to the versatility of the human voice. And as usual, the funk-filled, unpredictable beat is interesting enough to do justice to Gab.

There’s plenty on “The Craft” that could be overlooked. For one thing, the momentous raps go by so quickly that you’ll miss them without relatively close attention. And some treasures simply don’t come to light until the fourth or fifth listen. Like Timbaland — or to a lesser extent the Neptunes — Blackalicious’ second-half DJ Chief Xcel produces jarring yet always fascinating sonics by layering seemingly disparate sounds against one another. It’s well worth the many listens that it takes to pick the music apart.

“Your Move” starts out as a sparse, drum-and-hand-claps club track, but twangy, almost psychedelic electric guitars bubble up as major surprises. An even more satisfying shock is the synthesized trumpets that quiver sporadically in the background. Utilizing these rock ‘n roll fusion techniques is a daring gamble that pays off big time, elevating what could have easily been your average head-banger to another level entirely.

“Lotus Flower” is another musical marvel — and again the devil’s in the details. A standard-issue drum line and an only halfway catchy melody might not turn many heads at first, but listen deeper and you’ll be captivated by the futuristic laser bleeps buried under the chorus’ freaky yet restrained vocals. (Think Andre 3000 on opium watching an outer-space horror flick.)

That track also boasts a griminess that’s become an underground trademark, and has since been adopted by the South. Instruments are a bit more muffled, Fender Basses sound a bit thicker, and voices lack the handsomeness you’d expect from a rap star. At times on the album, one can almost hear a tension between the Xcel’s futuristic glitches and the propensity towards funk and grit.

Perhaps the album’s standout track is “Black Diamonds and Pearls,” if only because it has so much to say, and such an artful delivery. Gab slows down his flow to a comfortable trot, rapping about the broken spirit of impoverished African Americans over an exquisitely aged R&B sample. While mainstream rap albums usually supply leftover beats to their token message songs, Blackalicious gives “Diamonds” all the juice and energy of a would-be single.

It’s hard not to agree when he asks: “[You] talk about peace and love and God/ But then why are we at war?”

The album’s cohesiveness takes a downslide in the last few songs, with the atonal and nearly robotic “Give it to You,” and the sloppy, uncontrolled “Egosonic War Drums.” But these few off-the-wall missteps are excusable, and their presence almost heighten one’s appreciation of the heightened creativity that comes before.

“Underground hip-hop” is still a slippery, vague notion in the pop vernacular — and it’s arguable that the phrase’s more-popular cousin “indie-rock” has little more than negative connotations left. However they’re labeled, Blackalicious continues to innovate where the mainstream stagnates, venturing into far-off lands of poetry and funk. It’s delicious.