Method that returns description attribute of enum value
Type type = input.GetType();
   MemberInfo[] memInfo = type.GetMember(input.ToString());



You should use more meaningful variable names like enumType and enumMembers and your code could use some more LINQ and vars.




if (memInfo != null &amp;&amp; memInfo.Length &gt; 0)



This null check is unnecessary. The docs says about GetMember:


  An array of MemberInfo objects representing the public members with the specified name, if found; otherwise, an empty array.


So we can remove one null check and test only the description-attribute and turn it into a ternary operator:

public static string GetDescription(System.Enum value)
{
    var enumMember = value.GetType().GetMember(value.ToString()).FirstOrDefault();
    var descriptionAttribute = 
        enumMember == null 
            ? default(DescriptionAttribute) 
            : enumMember.GetCustomAttribute(typeof(DescriptionAttribute)) as DescriptionAttribute;
    return 
        descriptionAttribute == null 
            ? value.ToString() 
            : descriptionAttribute.Description;
}





  I think this code can be more elegant


With C# 6 it can be just a small chain of method calls...

public static string GetDescription(Enum value)
{
    return
        value
            .GetType()
            .GetMember(value.ToString())
            .FirstOrDefault()
            ?.GetCustomAttribute&lt;DescriptionAttribute&gt;()
            ?.Description
        ?? value.ToString();        
}