Glossary of Terms:

http://awstats.sourceforge.net/docs/awstats_glossary.html

Visits: (The Viewed)
Number of visits made by all visitors.
Think "session" here, say a unique IP accesses a page, and then requests three other pages within an hour. All of the "pages" are included in the visit, therefore you should expect multiple pages per visit and multiple visits per unique visitor (assuming that some of the unique IPs are logged with more than an hour between requests)

Bandwidth: (avg size)
Total number of bytes for pages, images and files downloaded by web browsing.
Note 1: Of course, this number includes only traffic for web only (or mail only, or ftp only depending on value of LogType).
Note 2: This number does not include technical header data size used inside the HTTP or HTTPS protocol or by protocols at a lower level (TCP, IP...).
Because of two previous notes, this number is often lower than bandwith reported by your provider (your provider counts in most cases bandwitdh at a lower level and includes all IP and UDP traffic).

Entry Page:
First page viewed by a visitor during its visit.
Note: When a visit started at end of month to end at beginning of next month, you might have an Entry page for the month report and no Exit pages.
That's why Entry pages can be different than Exit pages.

Exit Page:
Last page viewed by a visitor during its visit.
Note: When a visit started at end of month to end at beginning of next month, you might have an Entry page for the month report and no Exit pages.
That's why Entry pages can be different than Exit pages.