A tag is a reference to a sub unit in a program. A tag references syntactic elements like functions, classes e.t.c. A tags table consists of list of tag names and their positions in corresponding files.

A tags table can be generated by etags program. If you are using Ubuntu machine, you can install it with

sudo apt-get install exuberant-ctags

Now, you can generate tags for a file with

etags input_file

Depending on the project, we can also generate tags for a particular type. For example, we can generate tags for all python files using

find . -name '*.py' -exec etags -a {} \;

This tag tables enables you to jump to definition of any tag. You can place cursor on a tag and pressM-.(find-tag) which takes you to definition of that tag. If you want to go back to previous location, you can use M-*(pop-tag -mark). There are several functions which help to navigate tags.

ctags-update is a third party package which automatically updates TAGS file when new files are created.

In addition to them, helm provides a function called helm-semantic which shows all available tags in the current file. This works without TAGS file. Helm also has helm-etags-select which provides helm interface to select tags.

If you are working with a python projects, you can use elpy which navigates tags (using Jedi in the backend) without any TAGS file.