It depends on the slide guitarist's specific style.

   He may play acoustic or electric.

      If acoustic, he may play bottleneck or lap-style.

         If bottleneck, he may play on a regular acoustic guitar, a wood-bodied resonator guitar, or a metal-bodied resonator guitar.

         If lap-style, he may play on a modified regular acoustic guitar, a Dobro, or a Weissenborn style guitar.

   If electric, he also may play bottleneck or lap-style.

         If bottleneck, he may play on a regular electric guitar, or the amplified version of a resonator guitar.

         If lap-style, he may play on a lap steel or a pedal steel.

I count that to be ten different ways to play slide guitar. We slide players can't even make up our minds how it should be done and you want to know how many of us it takes to change a lightbulb?