MODULO 10^9 + 7 output.

The modulo operation is the same as  the remainder of the division .  a modulo b is c, means that the remainder when a is divided by b is c.It is represented by the ‘%’ operator in many programming languages.
For eg:
5%2=1

What is the necessary of MODULO 10^9+7 :

The largest integer data type in C/C++ is the long long int; its size is 64 bits and can store integers from ( –2^63 ) to ( +2^63 -1 ) . Integers as large as 9 X 10^18 can be stored in a long long int. But in problems like calculating the number of permutations of a size n array, even this large range may prove insufficient. We know that the number of permutations of a size n array is n!. Even for a small value of n, the answer can be very large. Eg, for n=21, the answer is 21! which is about 5 x 10^19 and too large for a long long int variable to store. This makes calculating values of large factorials difficult.

So, instead of asking the exact value of the answer, the problem setters ask the answer modulo some number M; so that the answer still remain in the range that can be stored easily in a variable.

Some languages such as Java and Python offer data types that are capable of storing infinitely large numbers. But in that case the time of execution will increase as the input size increase.

Two points should be considered while choosing M.  It should just be large enough to fit in an int data type. And it should be a prime number.

10^9 + 7 fits both criteria; which is why you nearly always find 10^9 + 7 in modulo type questions.