Dictionary is value type or reference type?

It is definitely a reference type.
It is because variables of dictionary store references to their data (objects).

Good question!
I have some confusing too.
Why in this code value will be null if I remove “ref” ?

public StatisticData()
{
    SetDefaultRecords(ref CommonRecords);
}
private void SetDefaultRecords(ref Dictionary<RecordName, string> dictionary)
{
    dictionary =
        Enum.GetValues(typeof(RecordName))
        .Cast<RecordName>()
        .ToDictionary(key => key, "");
}

Dictionary is a reference Type.

Reference Type because it has a reference of key and value

It is reference type.

Reference Type because it has a reference of key and value…

Reference Type

Value types - Stored on Stack. GC not required for it as it is holding value itself so no memory leak. Struct in C# are example of value type objects i.e. integer, bool and other data types except String(It is a class).

Reference Type - It is stored on Heap and GC is needed to clean unused objects in memory. Actual value is stored on Stack but that reference is stored on Heap. If you use GetHashCode() method on int object it will give you the value it contains. But when you use GetHashCode() method on class it givens you a hashcode, which is the memory address of that object. String is a class and a reference type.

Dictionary is a reference type
var countryCodes = new Dictionary(string, string) { {"IN", "India"}, {"JP", "Japan"} }

It’s reference type