Activity - An activity represents a single screen with a user interface

Fragment- In Android, the fragment is the part of Activity which represents a portion of User Interface(UI) on the screen. It is the modular section of the android activity that is very helpful in creating UI designs that are flexible in nature and auto-adjustable based on the device screen size.

Single frame fragments : Single frame fragments are using for hand hold devices like mobiles, here we can show only one fragment as a view.

List fragments : fragments having special list view is called as list fragment

Fragments transaction : Using with fragment transaction. we can move one fragment to another fragment.

Dialog Fragment - DialogFragment is a utility class which extends the Fragment class. It is a part of the v4 support library and is used to display an overlay modal window within an activity that floats on top of the rest of the content. Essentially a DialogFragment displays a Dialog but inside a Fragment

Intent - are used for navigating among various activities within the same application

Internal Intent. i.e. calling intended actions in same activity.

External Intent i. e. opening another activity after some operations like onClick

XML Parsing - XML stands for Extensible Mark-up Language.XML is a very popular format and commonly used for sharing data on the internet. thete are three types of XML parsers which are DOM,SAX and XMLPullParser. Among all of them android recommend XMLPullParser because it is efficient and easy to use.

JSON Parsing - JSON parsing is the process of converting a JSON object in text format to a Javascript object that can be used inside a program.

Shared Preferences - A SharedPreferences object points to a file containing key-value pairs and provides simple methods to read and write them.

Bundle- The App Bundle must include the application's compiled code and resources, which allows for the signing and generation of APK files to be deferred to the app store, reducing the initial download size of the app.

Context - An Android app has activities. Context is like a handle to the environment your application is currently running in. The activity object inherits the Context object.

putExtra - The main use of the putExtra() method is to send values you need in the next activity.

Adapter - In Android, Adapter is a bridge between UI component and data source that helps us to fill data in UI component. It holds the data and send the data to an Adapter view then view can takes the data from the adapter view and shows the data on different views like as ListView, GridView, Spinner etc.

Simple adapters - to map static data to views defined in our XML file(UI component)
Types: Base Adapter,ArrayAdapter

Layouts - A layout defines the structure for a user interface in your app, such as in an activity.
Types: Linear, Relative, Constraint, Grid, Table

Some Important Topics:
ListView
Spinner view
Custom ListView
GridView
Shared Preferences
Internal Storage
External Storage
SQLite
ImageView
Option Menu
Contextual Menu
PopUp Menu
Schedule Notification
Ping Notification
Expandable ListView
Custom Notification
Autocomplete

MultiAutocomplete
Textview

Different Alert Dialog
Passing Value from one Activity to Another
InboxStyle Notification
SetOnClickListener
find View By Id