Cell Reference

A string identifying a particular cell in a spreadsheet, possibly relative to the cell containing the reference. A cell reference may be absolute (denoted by a "$" prefix in Excel ) or relative (no prefix) in each dimension, thus, e.g. B$6 refers to the second cell across in the sixth row.

Single Cell- A1
Cell B1 and B2- B1,B2
Range from C1 to C5- C1:C5
Range from A1 to L1- A1:L1

Reference Types 
• Relative - automatically changes when the  formula is copied down a column or across a row 
• Absolute - cell reference is fixed, doesn’t  change when copied to other cells. 
• Uses $ sign like: $A$1 
• Mixed - has either an absolute column and  a relative row, or an absolute row and a relative column 

• Like A$1 or $A1

Referencing other the Sheet
• Same file 
         – Manual selection 
         – Use a formula 
         • Ex: Sheet2!A1 
• Different file 
          – Manual selection 
          – Use a formula 
        • Ex: [File2.xlsx]Sheet1!$A$1 

          •Absolute by default


Sources:
http://office.microsoft.com
http://moodle.pshs-brc.edu.ph