In algebra, we come across two types of symbols namely **constants** and **variables.**

Constant :- A symbol having fixed numerical value is called a **constant.**

**Ex:** 3, -2, 4, 0, 1/2, -5/3

**Variable or a Literal :-** A symbol which can take various numerical values is called a **variable** or a **literal.**

A symbol which takes on various numerical values is called a **variable or a literal**

* Which is the product of a constant and a variable is also a variable.

**Ex: 3x, -5y etc.**

A combination of two or more variables separated by + sign or a – sin is also a variable.

**Terms: **

* A constant or a variable or the product of a constant and a variable is called a **term.**

* Product of two or more terms is also called a term.

* Every constant or variable is called a term.

Ex: 3xy ; 2x^{2} y

**Algebraic Expressions: **

A combination of constants and variables, connected by the symbols +, -, × and ÷ is called an algebraic expression.

* The several parts of an expression separated by the sign + or- are called the terms of the expression.

* A single term or a group of terms with addition and subtraction operations is called an **expression.**

If every term of an expression is a constant term, such expression is called **numerical expression**.

Every numerical expression represents a number.

The expression containing at least one algebraic term is called an **algebraic expression.**

**Types of Algebraic Expressions:**

Algebraic expressions are categorized according to the number of terms in it.

**Monomial: **An algebraic expression which contains only one term is called a **monomial.**

Binomial: An algebraic expression which contains two terms is called a **binomial.**

Trinomial :- An algebraic expression which contains three terms is called a **trinomial.**

Multinomial:- An algebraic expression which contains two or more terms is called a **multinomial.**

**Like terms: **

The terms having same literal factors (coefficient) are called **like terms or similar terms.**

**Unlike terms: **

The terms not having same literal factors are called **unlike terms or dissimilar terms.**