There is a good overview on the Adobe Analytics Help Microsite (linked below). Visits cast a wider net comprehensive for the entire Visitor web session whereas Hit based segments are based off occurrences of page or link requests.
The Visitor container includes every visit and page view for visitors within a specified time frame. A segment at the Visitor level returns the page that meets the condition plus all other pages viewed by the visitor (and only constrained by defined date ranges). As the most broadly-defined container, reports generated at the Visitor container level will return page views across all visits and lets you generate a multi-visit analysis. Consequently, the Visitor container is the most susceptible to change based on defined date ranges.
Visitor containers can include values based on a visitor's overall history:
Days Before First Purchase
Original Entry Page
Original Referring Domains
The Visit container lets you identify page interactions, campaigns, or conversions for a specific web session. The Visit container is the most commonly used container because it captures behaviors for the entire visit session once the rule is met and lets you define which visits you want to include or exclude in building and applying a segment. It can help you answer the question of how many visitors viewed the News and Sports section in the same visit? Or pages that attributed to a successful conversion to a sale?
Visit containers include values based on occurrence per visit:
Linearly allocated metrics
The Hit container defines which page hits you would like to include or exclude from a segment. It is the most narrow of the containers available to let you identify specific clicks and page view where a condition is true, letting you view a single tracking code, or isolate behavior within a particular section of your site. You may also want to pinpoint a specific value when an action occurs, such as the marketing channel when an order was placed.
Hit containers include values based single page breakdowns: