Algol, short for "Algorithmic Language," is one of the earliest high-level programming languages, designed for scientific and numerical computation. It was developed in the late 1950s and first specified in 1958 by an international committee of European and American computer scientists. Algol was significant in the history of programming languages because it introduced many concepts that later became standard in other languages.

Key features of Algol include:

1. **Structured Programming:** Algol was one of the first programming languages to support structured programming concepts like nested blocks, conditional statements (if-then-else), and looping constructs (for, while).

2. **Block Structure:** Algol introduced the idea of program blocks, which allow for local scoping of variables. This concept influenced many subsequent programming languages.

3. **Backus-Naur Form (BNF):** Algol's syntax was described using a formal notation known as Backus-Naur Form, which later became widely used for describing the syntax of programming languages.

4. **Orthogonality:** Algol aimed for a high degree of orthogonality, meaning that the language was designed to have a relatively small number of primitive constructs that could be combined in a large number of ways.

5. **Portability:** Although Algol was not as widely implemented as some other languages, it had a significant impact on the design of subsequent languages, particularly Pascal and C.

Algol served as a basis for the development of many other programming languages, directly or indirectly influencing languages such as Pascal, C, and Ada. Though it is not widely used today, its influence on the development of programming language theory and practice is significant.