Meta SQL plays an important role on PeopleSoft language.It eases the complication involved in writing Platform specific code from developer prospective.
PeopleTools convert the Meta SQL into platform specific code at run time.

Thanks
Nitin Bhatia

Nitin is correct. Also, some meta sql like %select and %bind are almost always used in application engines. %select to assign values to variables and %bind to get that value from the variable. Another meta SQL that you see used most often is the %table. It is really easy and simple to use. Instead of writing your table name as PS_TABLE_NAME, you do the following %TABLE(TABLE_NAME).