Legislative Knowledge is...

العلم الشرعي، والمراد به : ((علم ما أنزل الله على رسوله من البيانات والهدى))

The Legislative Knowledge, and the desired by it (is): knowledge which Allah send on His Messenger sallallahu alayhe wa sallam from the clarifications and guidance!

--taken from the kitab Al-Ilm of Shaykh Uthaymeen, first chapter as found on his site in arabic--