Q1. What is a wordpress plugin?

1. A plugin in wordpress is basically a php script that helps in extending or altering the core functionality of the wordpress. There are various tools available in wordpress which can help building the customized wordpress plugins. Plugins when added or activated in wordpress can add a feature or set of features, to wordpress. There is not any limit set for what a plugin can do in wordpress. That’s why there are unlimited number of plugins available in wordpress

Q2. What are the different kinds of API’s (Application Programming Interfaces) available in wordpress or how plugin provide different API’s to interact with wordpress core?

1. 1. Plugin
2. Widgets : create and manage widgets in your plugin.
3. Shortcode
4. HTTP
5. Settings
6. Options
7. Dashboard Widgets
8. Rewrite
9. Transients
10. Database

Q3. How many types of hooks are there in wordpress?

1. Two types: Actions and Filters

Q4. What Plugins are made up of?

1. Plugins basically contains hooks that let the plugins to access specific parts of wordpress.

Q5. When Action hooks are triggered?

1. An action hook enables the user to trigger custom plugin code at specific points during execution For. eg. You can trigger a custom function to run after a user register a user account in wordpress.

Q6. When Filter hooks are triggered?

1. The filter hook modifies text before adding or after retrieving from the database.

Q7. Where widget menu appears? 

1. It appears under Appearance menu in dashboard

Q8. For what widgets are used?

1. Widgets are available to be added basically to be added on any registered sidebar in your theme.

Q9. Does a widget have multiple instances?

1. yes, so that they can be used with all the sidebars registered in your theme.