Query Chatter Feed Item & How the structure in Salesforce object

Salesforce admin can enable Chatter feed tracking on Salesforce objects, including custom objects.
Go to Setup and search for Feed Tracking in the Quick Find search box. Select the object to track and tick "Enable Feed Tracking", you can select up to 20 fields.

In the background, once an object is enabled for feed tracking, Salesforce will create a new object with the suffix Feed (for Standard object) or _Feed (for Custom object). This is available in API version 18.0 and later.

Sample query:

SELECT Id, ParentId, Type, RelatedRecordId, Title, Body, CreatedById, CreatedDate, CommentCount, LikeCount FROM AccountFeed ORDER BY CreatedDate DESC

This query will return all feed tagged to Account (see ParentId field)

Another object storing all feeds is FeedItem, this object is available in API version 21.0 and later, sample query
SELECT Id, ParentId, Type, RelatedRecordId, Title, Body, CommentCount, LikeCount FROM FeedItem ORDER BY ParentId

This query will return all feed tags to any objects.

See the architecture below (right-click the image to enlarge):

Notice that objectFeed object shared the same prefix with FeedItem: 0D5

If you need the screenshot in Visio file, click here