System collection encompasses many classes as listed below, this was obtained from Microsoft's site.

System.Collections Namespace 

The System.Collections namespace contains interfaces and classes that define various collections of objects, such as lists, queues, bit arrays, hash tables and dictionaries.

ClassesClasses

 

Class

Description

Public class

ArrayList

Implements the IList interface using an array whose size is dynamically increased as required.

Public class

BitArray

Manages a compact array of bit values, which are represented as Booleans, where true indicates that the bit is on (1) and false indicates the bit is off (0).

Public class

CaseInsensitiveComparer

Compares two objects for equivalence, ignoring the case of strings.

Public class

CaseInsensitiveHashCodeProvider

Supplies a hash code for an object, using a hashing algorithm that ignores the case of strings.

Public class

CollectionBase

Provides the abstract base class for a strongly typed collection.

Public class

Comparer

Compares two objects for equivalence, where string comparisons are case-sensitive.

Public class

DictionaryBase

Provides the abstract base class for a strongly typed collection of key/value pairs.

Public class

Hashtable

Represents a collection of key/value pairs that are organized based on the hash code of the key.

Public class

Queue

Represents a first-in, first-out collection of objects.

Public class

ReadOnlyCollectionBase

Provides the abstract base class for a strongly typed non-generic read-only collection.

Public class

SortedList

Represents a collection of key/value pairs that are sorted by the keys and are accessible by key and by index.

Public class

Stack

Represents a simple last-in-first-out (LIFO) non-generic collection of objects.

InterfacesInterfaces

 

Interface

Description

Public interface

ICollection

Defines size, enumerators, and synchronization methods for all nongeneric collections.

Public interface

IComparer

Exposes a method that compares two objects.

Public interface

IDictionary

Represents a nongeneric collection of key/value pairs.

Public interface

IDictionaryEnumerator

Enumerates the elements of a nongeneric dictionary.

Public interface

IEnumerable

Exposes the enumerator, which supports a simple iteration over a non-generic collection.

Public interface

IEnumerator

Supports a simple iteration over a nongeneric collection.

Public interface

IEqualityComparer

Defines methods to support the comparison of objects for equality.

Public interface

IHashCodeProvider

Supplies a hash code for an object, using a custom hash function.

Public interface

IList

Represents a non-generic collection of objects that can be individually accessed by index.

StructuresStructures

 

Structure

Description

Public structure

DictionaryEntry