How to understand unlimited hosting plan?

In unlimited hosting plans, what does unlimited really mean?

Bandwidth per month describes the amount limit of data transferred to or from the website or server within a month. For example 500 gigabytes per month. If the total amount of data downloaded from the website in a particular month reaches this limit, the hosting company may shut off further public access to the site, or hosting company may charge you for the ultra bandwidth using.
What does "unlimited bandwidth" really mean?
You should understand it as hosts try to provide as much bandwidth as they could to you. You will never be charged for ultra bandwidth using. The vast majority of clients will never need to worry about bandwidth.
But you should know that a shared web hosting service means a number of customers' web sites are hosted from the same server. To ensure that Web Hosting is reliable and available for the greatest number of users, a customer's web site usage cannot adversely affect the performance of other customers' sites.
So there are still some constraints on bandwidth using. Different hosts place differnet constraints on the bandwidth using.
Do read TOS carefully before you pay for your hosting plan.

Disk space refers to the amount of hard drive storage space you are allotted on a host Web server. The text, images, sound files, video files, and other elements that make up your website occupy storage space on a server.
What does "unlimited disk space" really mean?
You should understand it as hosts try to provide as much disk space as they could to you. You will never be charged for ultra disk space using. The vast majority of clients will never need to worry about disk space. But you should know that a shared web hosting service means a number of customers' web sites are hosted from the same server. To ensure that Web Hosting is reliable and available for the greatest number of users, a customer's web site usage cannot adversely affect the performance of other customers' sites. So there are still some constraints on the way you use disk space. Such as Using disk space primarily as an online storage space for archiving electronic files is prohibited in some hosting plans.
Different hosts place differnet constraints on the space using.
Do read TOS carefully before you pay for your hosting plan.