In Oracle stored procededures/queries the SQL used is PL/SQL. What do we call the SQL used in DB2 on WIndows/Linux/Unix?
It has some different ways of doing things
for eg.
The function NVL in PL/SQL is replaced by coalesce in DB2.
The method of writting recursive queries in Db2 (With...)is different from PL/SQL (Connect by prior)

So what exactly is this SQL Syntax called?

each supplier tries to stick to a certain standard (ansi/sql.....)
there are specific functions (not part of sql) available in each rdb that can do the same but have different names/syntax.
sql used in stored procedures is : sql procedure language sql/pl based on SQL

I read in some document that db2 uses Sql1999 std. Is this the same as the sql/PL standard mentioned by you?

sql/pl is just a procedure language that will use SQL
because sql is just select/update/insert... and not programming language as SQL/PL