Level 1 TLB Fills/sec is the frequency of faults that occur when reference is made to memory whose Page Table Entry (PTE) ...

Level 1 TLB Fills/sec is the frequency of faults that occur when reference is made to memory whose Page Table Entry (PTE) is not in the Translation Lookaside Buffer (TLB).  On some computers this fault is handled by software loading the PTE into the TLB, and this counter is incremented.