Load testing
Testing the application with maximum number of users and 
input.
Stress testing
Testing the application with more than the maximum number 
of users and input.

Load testing is the process of creating demand on a system
or application to measuring its response.

Stress testing is process used to determine the stability of
a given system or application.Like testing beyond normal
operational capacity, often to a breaking point, in order to
observe the results.

Load Testing:
Testing with maximun no. of users and systems

Stress Testing:
the application with more than the maximum number 
of users and input.

One of the most common, but unfortunate misuse of 
terminology is treating "load testing" and "stress testing" 
as synonymous. The consequence of this ignorant semantic 
abuse is usually that the system is neither properly "load 
tested" nor subjected to a meaningful stress test.

1. Stress testing is subjecting a system to an unreasonable 
load while denying it the resources (e.g., RAM, disc, mips, 
interrupts, etc.) needed to process that load. The idea is 
to stress a system to the breaking point in order to find 
bugs that will make that break potentially harmful. The 
system is not expected to process the overload without 
adequate resources, but to behave (e.g., fail) in a decent 
manner (e.g., not corrupting or losing data). Bugs and 
failure modes discovered under stress testing may or may 
not be repaired depending on the application, the failure 
mode, consequences, etc. The load (incoming transaction 
stream) in stress testing is often deliberately distorted 
so as to force the system into resource depletion.

2. Load testing is subjecting a system to a statistically 
representative (usually) load. The two main reasons for 
using such loads is in support of software reliability 
testing and in performance testing. The term "load testing" 
by itself is too vague and imprecise to warrant use. For 
example, do you mean representative 
load," "overload," "high load," etc. In performance 
testing, load is varied from a minimum (zero) to the 
maximum level the system can sustain without running out of 
resources or having, transactions suffer (application-
specific) excessive delay.

3. A third use of the term is as a test whose objective is 
to determine the maximum sustainable load the system can 
handle. In this usage, "load testing" is merely testing at 
the highest transaction arrival rate in performance testing