What is meant by Ems? (Android TextView)

ems is a unit of measurement

The name em was originally a reference to the width of the capital M. It sets the width of a TextView/EditText to fit a text of n 'M' letters regardless of the actual text extension and text size.

Eg :

android:ems Makes the EditText be exactly this many ems wide.

    android:ems="2"

/>

denotes twice the width of letter M is created.