What are Design Patterns?

what it is

Design patterns are optimized, reusable solutions to the programming problems that we encounter every day.
It is a template that has to be implemented in the correct situation.
"descriptions of communicating objects and classes customized to solve a general design problem in a particular context" - Erich Gamma

They are not algorithms or data structures

provide solutions to computational problems; patterns focus on non-functional issues like extendibility and maintainability

They are not programming idioms

they are reoccurring low-level solutions to common programming problems in a specific language; design patterns are high-level and language independent
idioms are looked at while coding; patterns at design time

They are not frameworks

design patterns are more general than frameworks and generative; frameworks are architectures that cannot generate solution

Structural patterns generally deal with relationships between entities, making it easier for these entities to work together.

Creational patterns provide instantiation mechanisms, making it easier to create objects in a way that suits the situation.

Behavioral patterns are used in communications between entities and make it easier and more flexible for these entities to communicate.

An anti-pattern is a common reaction to a recurring problem that is gleaned from bad experience

An anti-pattern usually results in an ineffective and risky solution that is likely to be counterproductive
A code smell is not buggy code
- it is technically correct code that does not prevent the program from functioning yet it may contribute to future technical failure
- it is a set of coding factors that indicates weaknesses in design that usually results in slowing down development, increasing risk of bugs, increasing difficulty in code maintenance and scalability