Definition and background:
This is a directive to perform an indicated note or passage of a composition one octave higher than notated. Typically, this is indicated by an 8va or 8 over the note or passage followed by a dotted line over the top of all notes to be transposed. The end of the dotted line has a downstroke indicating that the following notes should be performed as written. The directive loco ("at place") is often found at the end of an all' ottava passage that also directs the performer to perform the notes in their correct place or as written.See 8va, 8.See also 15ma, 15.
For more information on the music term "All' ottava" check out these other resources:
Wikipedia - Glossary of Musical Terminology
Virginia Tech Multimedia Music Dictionary
ORB -- Medieval Music Glossary