When viewing a record detail page (e.g. Contact detail) the related lists (e.g. Cases related list) shows a limited number of related records at a time.

So, if you have more than 5 (by default) Cases tagged to an Contact, in the Contact detail page, you will see Show m more » | Go to list (n+) ». By default a will be 5 and b is total number of the records.

You can scroll down to the bottom of page, and look for Always show me more records per related list or Always show me fewer / more records per related list if you have click more before (even in previous login).
Always show me more records:

Always show me fewer / more records:

Clicking more or fewer increases and decreases the default number 5 (by default) of related list records displayed for all object record detail pages for the logged in user. If you notice, when you click more or fewer link, in the URL, Salesforce will add parameters rowsperlist=m (e.g. https://ap1.salesforce.com/0039000000ojedc?rowsperlist=10), this parameter will show related list up to 10 records for all related list.
Note: This change will be permanent for the logged in user for all tab, and can increase the related list records up-to 100.