NOUN (3)

1. a decrease of transmitted power in a mechanical system caused by slipping;

2. decline from a standard level of performance or achievement;

3. failing to hold or slipping out of place;
- Example: "the knots allowed no slippage"

The Collaborative International Dictionary of English v.0.48:

Slippage \Slip"page\, n.
   The act of slipping; also, the amount of slipping.
   [1913 Webster]

WordNet (r) 3.0 (2006):

slippage
    n 1: a decrease of transmitted power in a mechanical system
         caused by slipping
    2: decline from a standard level of performance or achievement
    3: failing to hold or slipping out of place; "the knots allowed
       no slippage"