What does API level mean?

Solution 1:

This actually sums it up pretty nicely.

API Levels generally mean that as a programmer, you can communicate with the devices' built in functions and functionality. As the API level increases, functionality adds up (although some of it can get deprecated).

Choosing an API level for an application development should take at least two thing into account:

1. Current distribution - How many devices can actually support my application, if it was developed for API level 9, it cannot run on API level 8 and below, then "only" around 60% of devices can run it (true to the date this post was made).
2. Choosing a lower API level may support more devices but gain less functionality for your app. you may also work harder to achieve features you could've easily gained if you chose higher API level.

Android API levels can be divided to five main groups (not scientific, but what the heck):

1. Android 1.5 - 2.3 (Cupcake to Gingerbread) - (API levels 3-10) - Android made specifically for smartphones.
2. Android 3.0 - 3.2 (Honeycomb) (API levels 11-13) - Android made for tablets.
3. Android 4.0 - 4.4 (KitKat) - (API levels 14-19) - A big merge with tons of additional functionality, totally revamped Android version, for both phone and tablets.
4. Android 5.0 - 5.1 (Lollipop) - (API levels 21-22) - Material Design introduced.
5. Android 6.0 - 6.… (Marshmallow) - (API levels 23-…) - Runtime Permissions,Apache HTTP Client Removed

Solution 2:

API level is basically the Android version. Instead of using the Android version name (eg 2.0, 2.3, 3.0, etc) an integer number is used. This number is increased with each version. Android 1.6 is API Level 4, Android 2.0 is API Level 5, Android 2.0.1 is API Level 6, and so on.

Solution 3:

An API is ready-made source code library.

In Java for example APIs are a set of related classes and interfaces that come in packages. This picture illustrates the libraries included in the Java Standard Edition API. Packages are denoted by their color.