Menzenchin

A hand is menzenchin 「門前清」, menzen for short, or "closed" in English, when it has not called on another player's discarded tile. This means the player has not called chii, pon, or an open kan. A closed kan (kan when drawing all 4 tiles yourself) does not break menzenchin. Only closed hands can score certain yaku.

A hand that is not closed is known as an open hand. This would be a hand that has called chii, pon, or an open kan. If a hand is open, it cannot score some yaku, and other yaku are reduced in value. While an open hand is usually less valuable than a closed one, but it has the ability to use chii and pon to complete faster.

Yaku

Closed Only

These yaku can only be scored closed; they cannot be scored with an open hand.

1 han		2 han	3 han
Riichi	Iipeikou	Double riichi	Ryanpeikou
Ippatsu	Pinfu	Chiitoitsu
Menzen tsumo

Kuisagari

Kuisagari 「喰い下がり」 is a property of some yaku to lose value when called open. Each yaku affected by kuisagari loses 1 han when opened.

From 2 han to 1 han	From 3 han to 2 han	From 6 han to 5 han
Sanshoku	Honitsu	Chinitsu
Ittsu	Junchan
Chanta

Open

These yaku are unaffected by the hand's open/closed status.

1 han	2 han
Tanyao*	Sanankou	Shousangen
Yakuhai	Sanshoku doukou	Toitoi
	Sankantsu

* Assuming kuitan (open tanyao) is enabled.

In addition, any yakuman that can be scored open do not lose value if opened.