Django CharField vs TextField
It's a difference between RDBMS's varchar (or similar) — those are usually specified with a maximum length, and might be more efficient in terms of performance or storage — and text (or similar) types — those are usually limited only by hardcoded implementation limits (not a DB schema).
PostgreSQL 9, specifically, states that "There is no performance difference among these three types", but AFAIK there are some differences in e.g. MySQL, so this is something to keep in mind.
A good rule of thumb is that you use CharField when you need to limit the maximum length, TextField otherwise.
This is not really Django-specific, also.
In some cases it is tied to how the field is used. In some DB engines the field differences determine how (and if) you search for text in the field. CharFields are typically used for things that are searchable, like if you want to search for "one" in the string "one plus two". Since the strings are shorter they are less time consuming for the engine to search through. TextFields are typically not meant to be searched through (like maybe the body of a blog) but are meant to hold large chunks of text. Now most of this depends on the DB Engine and like in Postgres it does not matter.
Even if it does not matter, if you use ModelForms you get a different type of editing field in the form. The ModelForm will generate an HTML form the size of one line of text for a CharField and multiline for a TextField.
For eg.,. 2 fields are added in a model like below..
description = models.TextField(blank=True, null=True)
title = models.CharField(max_length=64, blank=True, null=True)
Below are the mysql queries executed when migrations are applied.
for TextField(description) the field is defined as a longtext
ALTER TABLE `sometable_sometable` ADD COLUMN `description` longtext NULL;
The maximum length of TextField of MySQL is 4GB according to string-type-overview.
for CharField(title) the max_length(required) is defined as varchar(64)
ALTER TABLE `sometable_sometable` ADD COLUMN `title` varchar(64) NULL;
ALTER TABLE `sometable_sometable` ALTER COLUMN `title` DROP DEFAULT;