what differentiates in 2/12 way and 3 way speaker ?

Imagine a 3-way with 2 woofers.  If the crossover rolls off one woofer to mate with the midrange but rolls off the other at a lower frequency, it becomes a 2 1/2 way.

Much too general a statement. Only worry about how a speaker sounds not how it gets there.

      I agree!

My speakers are two way with 2 15'' woofers with a horn above said woofers. The crossover is 1000 Hz @ 12 dB per octave. It has three drivers but is still a two way speaker.

Mike

kr4 thank you for your explanation

Here is the layman's explanation as I see a 2 1/2 way.  Of course you have your tweeter.  Then you have two identical mid woofers.  One mid woofer reproduces high to lowest mid-range, the second reproduces only the lowest mid-range frequencies. 

But at least in my case, both the mid-woofers are exactly the same speaker models..

Earlier, I posted this too quickly and in error:

Imagine a 3-way with 2 woofers.  If the crossover rolls off one woofer to mate with the midrange but rolls off the other at a lower frequency, it becomes a 2 1/2 way.

Here are two correct alternative re-statements:

Imagine a 3-way with 2 woofers.  If the crossover rolls off one woofer to mate with the midrange but rolls off the other at a lower frequency, it becomes a 3 1/2 way.

Imagine a 2-way with 2 woofers.  If the crossover rolls off one woofer to mate with the tweeter but rolls off the other at a lower frequency, it becomes a 2 1/2 way.