ultrasonic and sonar?

[Trumpkin]

What is the difference between a sonar sensor and an ultrasonic sensor. Are they the same thing? Which one is better?

[Steve Joblin]

I am sure that someone will note some small definitional difference, but for the most part, with regards to robotics, and the companies that make the sensors, they are one in the same.

[Rebelgium]

exactly what steve said...

[bukowski]

well, if you wanted a small definitional difference, here ya go! 
Sonar (Sound Navigation And Ranging) is typically associated with underwater acoustics, and it is common to find low and mid frequency sonars that are audible to the human ear (eg you can hear the "ping" of a sonar against a subarine hull), but there are ultrasonic sonars also, like the ones used to find fish on a fishing boat.
Ultrasonics are the frequencies above the level of human hearing, >20Khz.

[Trumpkin]

Thanks, that had been bugging me .