Android Security Patch
Android has grown rapidly during past few years when the galaxy series of Samsung has been launched, hence increases the need for its security.
Android being made on Linux based kernel hence is free from viruses and malware until you download applications from a trusted source like google play store.
Beside this Android’s source code is not that much perfect which we want, just like the other OS source code it also has some of the vulnerabilities which are a threat for the Android users, which must be removed so as to provide a secure OS for the users.
For this google starts pushing some patches for the known vulnerabilities in the present (current) running Android source code, these pushing of patches are called Android Security Level.
Here Level means the date of the security patch, the latest the date is the more accurate security patch you will have.
Google started this trend from android marshmallow onwards.
For knowing your Security Patch Level.
Go to settings -> About phone.
You will see your Android Security Patch Level.