What do you mean by entity and bundle in drupal?

It is better to explain concepts of entity type, bundle, field and entity rather than only entity and bundle.

Entity Type: An entity type is a useful abstraction to group together fields. Let's consider some examples of entity types:

• Nodes

• Comments

• Taxonomy terms

• User profiles

Bundle: Bundles are an implementation of an entity type to which fields can be attached. You can consider bundles as subtypes of an entity type. With content nodes, for example, you can generate bundles like articles, blog posts, or products. Not all entity types have bundles, however. For example, users do not have separate bundles. For the entity types that do allow bundles, you can create as many bundles as you want. Then, using the Field system, you can add different fields to each bundle. Examples include a file download field on Basic Pages and a subtitle field on Articles

Field: A field is a reusable piece of content. In technical terms, each field is a primitive data type, with custom validators and widgets for editing and formatters for display. What's important to know as it relates to Entities is that Fields can be added to any of the bundles to help organize their data.

Entity: An entity would be one instance of a particular entity type such as a comment, taxonomy term or user profile or a bundle such as a blog post, article or product.