Does tailless means no tail at all? When I was reading about the HAL Tejas I observed that it was described as a "tailless" plane. However I could see a tail in the picture.

After careful reading I am assuming that being tailless means not having any tail planes a.k.a horizontal stabilizers.

Does tailless means no tail at all?
Tailless means no horizontal tail, but a vertical tail is still allowed. Examples are the Convair F-102 or Convair B-58.



Convair B-58 Hustler (picture source)

Compare this to a flying wing: Here even the vertical tail is left off. Since a classic delta would have too little lever arm for yaw control, this requires a higher aspect ratio wing. An example is the Horten IX:



Horten IX V1 prototype aircraft (picture source)