In most cases, SAP Business One allows you to change the name of the stock fields. This ability is extremely useful and can be used to do some interesting things.
To rename a field you simply control+double click the text label of the field. This will bring up a box that looks like this:
In the box titled "New Description" you would type the new name of the field you are changing. If you would like to revert the changes made to the field, click the restore defaults button. This will re-name the field to the original SAP Business One name.
Also included on this screen is the ability to make a field name appear in bold or with italics. Make your required changes and click update to commit them. You always have the option to restore the default SAP Business One field names at any time.
Keep in mind that changing a stock business one field will take affect for every user, so be sure to only give authorization to administrator level users. The correct authorization is called "Renaming Fields" under the "General" subheading. A user must have full authorization to make changes.
Being able to rename stock fields is very useful in setting up your system for how your business works. SAP Business One says each item is called "Item Number" but maybe your company is used to calling them SKU's or codes. Go ahead and change the field names to things that make sense. This will not change the core functionality of SAP Business One, it is purely cosmetic.
Another great idea for re-naming fields is the ability to repurpose stock SAP Business One fields. A popular example would be utilizing the "Foreign Name" field in the business partner master. This field holds a prominent piece of real estate on a business partner card and in most instances will never be used. Instead try re-naming it to "Old System Act#" allowing it to be used in searching for business partners using your old ERP system's account numbers. There are dozens of opportunities to use this trick for a cheap, effective, customization.
One disadvantage of utilizing stock fields for other purposes is that it may get confusing in query or customization. The underlying database fields will not change, it is purely cosmetic. In most cases, using these renamed fields in queries will retain their stock name making it a touch confusing. Just spend time making sure the users know this and it will become second nature in no time.