1.

Attitude - An signal to encourage/discourage continuation of partner's suit lead based on the rank of the card played, typically Standard Attitude.  Also see Upside Down Count and Attitude (UDCA) and Smith Echo

2.

Suit Preference - A signal indicating partiality of a certain suit based on the rank of the card played.  See Odd-Even, Lavinthal, Standard Attitude, Upside Down Count and Attitude (UDCA), Trump Suit Preference, and obvious suit preference

3.

Count - A signal showing the parity of a given suit as either an even or odd holding.  See Standard Count, Upside Down Count and Attitude (UDCA)

4.

Leads - Leads showing a sequence, such as leading the top of touching honors, other Opening Leads, fourth best or third and fifth leads, Journalist Leads, bottom of something and top of nothing, coded 9 and 10 (Jack denies, 10 implies), obvious suit preference, and Middle Up Down (MUD).