what does it mean to say a line it sleeved or needing to sleeve a line?

there is only one type of kite line that i know of that does not need to be sleeved.... q powerline

all other lines have the termination points sleeved.... the sleeve is an extra layer of fabric that acts as a protective barrier. if line were unsleeved, the friction coused by kite flying would cause the dyneema to melt.

As Dylan said. Spectra and Dyneema line are extremely strong; 10 times stronger than steel of the same diameter. But, they both have an extremely low melting point. When you put a knot in one of these lines the tension from the knot bearing down on one tiny spot of the line with full force will build up friction which will actually melt the line in half. Knotting Spectra or Dyneema line has been stated to reduce the strength of the line by as much as 50%. That means that if you knot a 600# line, the line could break with only 300# of tension on it.

Sleeving the line is the process of sliding the spectra line through a hollow sleeve material, usually dacron or other material that has a very high melting point. Putting a knot on the sleeving material will help reduce the loss of strength of the line at the knot. Dacron sleeving has been said to only reduce the overall strength of the line by only 10% or less. So, with sleeving you will see close to the full strength of the line without the loss of strength due to the knot.

If you are having problems with your lines breaking at our around the knot then sleeving the lines will probably help keep this from happening.

Hope that helps.