A way to join LEGO parts permanently, so they can't be separated ever again. Which is as horrible as it sounds.
A lot of LEGO purists frown upon the usage of glue (using a very loose definition of "frown upon" usually ranging from "not talking to those who do at all" to "wanting to hurt them phsyically").
However, there are some cases in which a LEGO model is regarded as built once and then never disassembled again, in which case gluing it may help making sure is stays together. Examples include:
- hobbyists regarding LEGO models the same way regular modelmakers do
- outdoors models which need to be more resistant to the elements
- publicly accessible models that prying hand of children can reach
- LEGOland parks models (which fit both categories above)
So you'll want to use this tag when asking specific questions on gluing models, such as in these example cases. Questions may range from asking the best type of glue to use depending on the case and its characteristics, how to remove glue, how to join a Gluers Anonymous group (or maybe not).
OK, seriously, don't glue LEGO elements. Just don't. The very fact that you made it to this page worries me a lot, you know?