'Datatype' is a attributes or format of the type of data that a column can hold in a table. It is related to objects as well.

Datatypes

The 'Datatypes' can be of type integer data, character data, monetary data, date and time data, binary types, unicode strings etc. When a particular column is defined as a particular datatype, it means that it will only accept data that follows certain characteristics pertaining to that datatype. In SQL Server, The datatypes are classified into the following:

• Number types
• Character strings
• Unicode strings
• Date types
• Binary types
• Other data types

The Data Types

Data Type	From	To	Space	Remarks
bit	0	1	1 to 8 bit columns in same table= 1 byte, 9 to 16 bits = 2 bytes,etc..
tinyint	0	255	1 byte	Whole numbers between the given range
smallint	-32,768	to 32,767	2 bytes	Whole numbers between the given range
int	-2,147, 483,648	2,147,483,647	4 bytes	Whole numbers between the given range
bigint	-9,223,372, 036, 854,775,808	9,223,372,036,854, 775,807	8 bytes	Whole numbers between the given range
decimal (precision, scale type)			5-17 bytes	The maximum total number of decimal digits that can be stored, both to the left and to the right of the decimal point. The precision must be a value from 1 through the maximum precision of 38. The default precision value is 18 The precision expression in the decimal indicates the maximum length of digits that can be stored (both to the left and to the right of the decimal point). Precision has a default value of 18 and ranges from 1 to 38. The scale expression in the decimal indicates the maximum length of digits stored to the right of the decimal point. Scale has a default value of 0 and ranges from 0 to precision's value.
numeric (precision, scale type)			5-17 bytes	The maximum total number of decimal digits that can be stored, both to the left and to the right of the decimal point. The precision must be a value from 1 through the maximum precision of 38. The default precision value is 18 The precision expression in the decimal indicates the maximum length of digits that can be stored (both to the left and to the right of the decimal point). Precision has a default value of 18 and ranges from 1 to 38. The scale expression in the decimal indicates the maximum length of digits stored to the right of the decimal point. Scale has a default value of 0 and ranges from 0 to precision's value.
smallmoney	-214,748.3648	214,748.3647	4 bytes
money	-922,337,203,685, 477.5808	922,337,203,685, 477.5807	8 bytes
float	-1.79E + 308	1.79E + 308	4 bytes when precision is < 25 and 8 bytes when precision > 25.	Precision is specified from 1 to 53
real	- 3.40E + 38	3.40E + 38	4 bytes	Precision is specified from 1 to 53
char	0 characters	8000 characters	storage size is the defined length.	Character string defined as char (n) where n is the string length
nchar	0 characters	4000 characters	storage size is the defined length.	Unicode string defined as nchar(n) where n is the string length
varchar	0 characters	8000 characters	storage size is the actual length of the data entered + 2 bytes	Character string defined as varchar( n ) where n is the string length
varchar(max)	0 characters	8000 characters	storage size is 2GB	Character string defined as varchar( max ). To be used when the size of the column data varies considerably and the size might exceed 8,000 bytes
nvarchar	0 characters	4000 characters	storage size is two times the actual length of the data entered + 2 bytes	Unicode string defined as nvarchar( n ) where n is the string length
nvarchar(max)	0 characters	4000 characters	storage size is 2GB	Character string defined as nvarchar( max ). To be used when the size of the column data varies considerably and the size might exceed 8,000 bytes
text	0 characters	2,147,483,647 characters	storage size is number of characters + 4 bytes	Do not use this as it is getting phased out in future versions of SQL Server. Use varchar(max) instead
ntext	0 characters	1,073,741,823 characters	storage size is 2 times the string length entered	Do not use this as it is getting phased out in future versions of SQL Server. Use nvarchar(max) instead
image	0 bytes	2,147,483,647 bytes		Do not use this as it is getting phased out in future versions of SQL Server. Use varbinary(max) instead
binary	0 bytes	8000 bytes	Storage size is the length defined	Defined as binary( n ) where n is the length defined in bytes.
varbinary	0 bytes	8000 bytes	Storage size is the length defined	Defined as binary( n ) where n is the length defined in bytes.
Smalldatetime	1900-01-01 00:00	2079-06-06 23:59	4 bytes	Accuracy is one minute
datetime	January 1, 1753 00:00:00	December 31, 9999 23:59:59	8 bytes	Accuracy is 007 seconds
datetime2	0001-01-01 00:00:00	9999-12-31 23:59:59	6 bytes	Accuracy is 100 nanoseconds
date	0001-01-01	9999-12-31	3 bytes	Accuracy is one day
time	00:00:00.0000000	23:59:59.9999999	5 bytes	Accuracy is 100 nanoseconds
datetimeoffset	0001-01-01 00:00:00	9999-12-31 23:59:59	10 bytes	Time zone offset range ia -14:00 through +14:00. Accuracy is 100 nanoseconds.
cursor				contains a reference to a cursor
sql_variant				various SQL Server-supported data types values can be stored in this data type
HierarchyId				can store values that represent nodes in a hierarchy tree.
uniqueidentifier			16 bytes	It is a unique identifier column holding a GUID string of 32 random characters in blocks separated by hyphens.
xml			2 GB	it helps SQL Server hold XML data in a column.
table				It can store the resultset of T-SQL statements for processing to be done later. It is used in user defined functions(UDF).
geometry				It allows you to store planar data about physical locations (distances, vectors, etc..
geography				It allows you to store round earth data such as latitude and longitude coordinates.