Is there a load testing of a mobile app?
Short answer: Yes there is.
Long answer: Well you can test the performance of your app on the device. You can test,
How much memory it occupies?
How much battery does it utilize?
What happens if you have several other apps open and then open your app?
Does it hang up the phone?
How much time does it take to process a request?
How does it work on low speed networks?
Well then you come to the server side. Here you can use tools like Jmeter. For this you will have to get the HTTP(s) requests your app makes and then you can generate a load for the same request. BUT That is for your server. If the server fails to handle the load, your app will receive ERROR 500 from the server.
So can we say load testing of a mobile app is Load testing of Web
Answer: If your app makes HTTP requests to a remote server interacts with it using some sort of web service then yes you can say that.
If not which tools can we use to test load on an Mobile App?
Answer: Like I said above you can use tools like Jmeter to do load testing for your http(s) requests.