What is Fragment ? *A Fragment represents a behavior or a portion of user interface in an Activity . *You can combine multiple fragments in a single activity to build a multi-pane UI and reuse a fragment in multiple activities. *fragment as a modular section of an activity , which has its own lifecycle, receives its own input events, and which you can add or remove while the activity is running * A fragment must always be embedded in an activity and the fragment's lifecycle is directly affected by the host activity's lifecycle. * For example, when the activity is paused, so are all fragments in it, and when the activity is destroyed, so are all fragments. *When you perform such a fragment transaction , you can also add it to a back stack that's managed by the activity—each back stack entry in the activity is a record of the fragment transaction that occurred. The back stack allows the user to reverse a frag...