A crossover domain in Maximo 7 is a value list that copies not only the selected value, but also related data to the record you opened the value list from. An easy example is the Asset field on a work order. When you select an asset, Maximo also copies the priority from the asset to the Priority field on the work order. This happens because there is a crossover domain for this. Take a look at it: in the application Domains, search for ASSET2WO.
How it is stored: Maximo stores labels in multiple places. When you add a label to a field, tab or section in Application Designer, Maximo stores this in the application XML in the MAXPRESENTATION table and in the MAXLABELS table. For fields, there are also labels stored in Database Configuration, in the title field on the attribute.
You probably ran into this problem when using Maximo: Maximo sometimes does not display all the characters in a field, because the text box is too small. Of course, you can solve this. First you need to understand how Maximo determines the display size of the text box. Then you can change these setting and control how large the text box should be.