Flanking

• (p. pr. & vb. n.) of Flank
Found on http://thinkexist.com/dictionary/meaning/flanking/

Flanking

When a creature with flanking is blocked by a creature without this ability, the blocking creature gets -1/-1 until end of turn. The effect is cumulative; multiple instances of flanking will effect a greater penalty, though a blocking creature only needs one instance to avoid the effect. Flanking first appears in the Mirage block.
Found on http://en.wikipedia.org/wiki/List_of_Magic:_The_Gathering_keywords#Typecycl
No exact match found