What is the difference between DIP and DIL ?

[Simon]

Just wondering. I think I see more of DIP in reference to IC's and DIL in reference to their sockets, is there any real difference ?

[Monkeh]

Dual In-Line and Dual In-line Package. So.. none. At all.

[mikeselectricstuff]

sometimes the P refers  to  Plastic, so a ceramic part is DIL but not DIP, but these are so rare nowadays that in practice the two terms are equivalent.

[Monkeh]

sometimes the P refers  to  Plastic, so a ceramic part is DIL but not DIP, but these are so rare nowadays that in practice the two terms are equivalent.

I thought that's what prefixes (PDIP, CDIP) were for.

[mikeselectricstuff]

sometimes the P refers  to  Plastic, so a ceramic part is DIL but not DIP, but these are so rare nowadays that in practice the two terms are equivalent.

I thought that's what prefixes (PDIP, CDIP) were for.

Sometimes yes, but in the early days there were a few different conventions which have stuck around or not in varying degrees.
Interestingly SIL is much more common than SIP for single-in-line. 

[ptricks]

DIP is for IC .
DIL is for anything that has dual rows of pins and can be anything from sockets to relays.

[george graves]

no difference at all.

[Kremmen]

sometimes the P refers  to  Plastic, so a ceramic part is DIL but not DIP, but these are so rare nowadays that in practice the two terms are equivalent.

Exactly this is my recollection as well. Industrial/mil rated dual-in-line chips and UVEEPROMS of the 27xxx family used to come in ceramic/cemented (DIL) packages that were said to be hermetic. Hermetic seal was not claimed for the ordinary plastic packages (DIP). Nowadays nobody seems to pay much attention to that distinction any more and anyway the ceramic slabs are all but gone anyway.