1. In network language, "d" is usually short for "de". For example, "Hello friend D" can be understood as "Hello friend".

2. In some social networks or chat applications, "D" can also be used as an emoticon, indicating the shape of a smile or mouth. For example, ":)" can be understood as a smiley face emoticon, while ":d" means a more exaggerated smile.

3. In some programming languages, "d" can be used as the name of a variable, function or class. For example, D language is an object-oriented programming language, and its name begins with "D".

4. In some cases, "D" can also be used as a scoring method, which usually stands for "bad review" or "low score". For example, on some e-commerce websites, users can rate a product, where "D" may represent a one-star or two-star rating.

Use of d:

1 stands for number: in English, d can stand for the number 500, which is the abbreviation of "500". For example, "$5d" means "500 dollars".

2. Representation of date: in the representation of date, d usually represents the date in the month, for example, "5d" means "5th".

3. stands for distance: in geography and mathematics, d usually stands for distance. For example, "d=vt" means "distance equals speed times time".

4. Indicating drug dosage: In medicine, d usually indicates drug dosage, for example, "qd" means once a day.