Lisp stands for LISt Processing. Elisp is the dialect of Lisp used in emacs, a text editor.

In Lisp, both data and programs are represented the same way: they are both lists of words, numbers, or other lists, sparated by whitespace and surrounded by parentheses.

Parts of lisp

Lisp programs are made up of expressions: lists or single atoms
Atoms are multi-character symbols, like forward-paragraph, single character symbols like +, strings of characters between double quotation marks, or numbers. Arrays are also considered to be an atom. Any object that is not a Cons Cell is an atom.
Made up of zero or more atoms or inner lists, separated by whitespace and surrounded by parentheses. A list can be empty.
Between quotation marks
Looks like a word. A name that can have a value attached to it just as it can have a function definition attached to it. It can have both at the same time. Or it can have just one or the other.
Evaluates to itself.
A set of instructions to the computer that tell the computer to do something
A symbol that is not quoted and that doesn't have parentheses around it. We bind a variable to a value.
Special forms
Some functions are unusual and do not work the usual manner. They are called special forms. Used for special jobs like defining a function, or 'if'.
A single-quote ‘'’ tells the Lisp interpreter that it should return the following expression as written, and not evaluate it as it would if the quote were not there.
A construct which differs from a function in that it translates a lisp expression into another expression that is to be evaluated in place of the original expression, e.g. 'when'.
Argument (of a function)
Information passed to the function. Atoms or lists that follow the function.
A function to determine whether some preperty is true or false.
It starts with ;
Interactive function
A function we evaluate by typing M-x or through a key or keychord.
Place where we do things. It's not a file, but it can be visiting a file.
car (first)
Reports what the first item in the list is.
cdr (rest)
The part of the list that follows the first item.
Cons cell
An object that consists of two slots, the car slot and the cdr slot. Each slot can hold any lisp object.
A series of cons cells, linked together so that the CDR slot of each cons cell holds either the next cons cell or the empty list.
Dotted pair notation
General syntax for cons cells that represents the CAR and CDR explicitly. (a . b) stands for a cons cell whose car is the object a and whose CDR is the object b.
Association list
Alist records a mapping from keys to values. It is a list of cons cells called associations. The CAR of each cons cell is the key, and the CDR is the associated value.
Collection of one or more files, formatted and bundled in such a way that users can easily download, install, uninstall and upgrade it.

Evaluating parts of lisp

Useful functions

Other things

Emacs specific functions