Export :        

1. It is used to export the Salesforce Data(excluding recycle bin's data) into your local  system.

2. You can export data from Salesforce using various tools, such as Data Loader, Salesforce Connect, or the Salesforce REST API.

3. The exported data can be saved in a variety of formats, including CSV, Excel, XML, or JSON. 

4. You can also customize the data you want to export by selecting specific objects, fields, and filters.

Export All : 

1. It is used to export the Salesforce Data(including recycle bin's data) into your local system.

2. When you choose the Export All option, Salesforce will create a .zip file containing all the data from your organization. 

Hard Delete :

1. In Salesforce, a hard delete is the permanent removal of a record and its associated data from the Salesforce database. 

2. When a record is hard-deleted, it cannot be restored or recovered, and all its associated data, such as related records, attachments, and files, are also permanently removed.

3. By default, Salesforce doesn't allow hard deletes of records, and instead, it uses a soft-delete mechanism. 

4. When a record is deleted, it is moved to the Recycle Bin, where it is stored for a certain period of time before being permanently deleted. During this time, users with the appropriate permissions can still recover the deleted record and its associated data from the Recycle Bin.