Letters or characters. Used to be 8-bit ASCII or ANSI, now 16-bit Unicode. Limit the number of characters in a database field to the maximum likely to be required.
Text may be encoded, that is shortened for ease of entry and more compact storage, for example the world's airports have three-letter codes, LHR, LGW, LAX, JFK, etc.
Where there is a limited number of text items, such as the positions in football, a lookup table may be used where the six or so items appear in a list from which the user can choose. Such lists can be much longer than 6 items if required.
Numbers include integers (1,2,3...), real or floating point (3.14159...) and currency (£34.56).
Where text and numbers are mixed e.g. most pieces of text e.g. Wikipedia.
Telephone numbers are usually defined as text as they need a leading zero (suppressed in numeric format) and no mathematical operations are performed on them.
ISBN numbers (on books) are digits but are stored as text because they can include a character as a check digit - if the check digit is 10 then it appears as 'X'.
These are structured types as they consist of more than one part: day, month, year; hours, minutes, seconds, milliseconds. They are actually stored as simple numbers and the various parts are calculated from a base value. In MS products day 1 is 1/1/1900 so 7/12/2007 is 39,423 as this date is 39,423 days after 1/1/1900.
These can have the values Yes/No or True/False. This takes up less space than the text fields 'Yes' and 'No' and can be represented by a tick box with two states.
A field is an atomic data item, that is it cannot be broken down further into smaller parts (unless you count characters and digits). For example 'LastName', 'DateOfBirth' and 'Salary' are all examples of fields
A key field is a field that uniquely identifies a record so that it cannot be mistaken for something else. A key field is often known as the primary key. Name is generally inadequate as a key field because two or more people can have the same name. Unique identifiers include things like bank account numbers, national insurance numbers, health system numbers and passport numbers. Where there is no obvious primary key in a record it is easy to add one as an 'auto number'.
A record is a group of fields that are logically connected, for example they are facts about a person or a car.
A file is a collection of records that are logically related, for example a series of records in a file of employees or child benefit claimants (that has been lost in the post).
A database program has fields and records but the file is hidden from the user as a collection of tables, forms, queries, reports, etc.