An expression is a sequence of

1. one or more operands, and
2. zero or more operators

that can be evaluated into some value (Docs, 2017).

In C#, expressions can consist of

1. literal value
   • 1, “abc”
2. method invocation
   • CallMe()
3. operator and operands
   • 1 + 2 - 3
4. simple name
   • variable: num, age
   • method parameter: CallMe(myNumber)

There are also other types of expressions, for example:

1. LINQ query expressions (Docs, 2016)

    IEnumerable<int> scoreQuery =
        from score in scores
        where score > 80
        select score;
   

2. lambda expressions, (int x, string s) => s.Length > x

References

1. Docs, M. (2017, May 11). Expressions (C# Programming Guide). Retrieved from https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/statements-expressions-operators/expressions
2. Docs, M. (2016, November 30). Language Integrated Query (LINQ). Retrieved from https://docs.microsoft.com/en-us/dotnet/csharp/linq/index