Altera is a company that makes a special type of computer chip called a Field Programmable Gate Array (FPGA). An FPGA is a chip that can be programmed to do all sorts of different things, and it's used in many different kinds of electronics. For example, it might be used in a television to decode the signal that's coming in from an antenna, or in a car to control the air conditioning system.
In order to program an FPGA chip, you need to use a special language called Hardware Description Language (HDL). HDL is a way of telling the chip what to do by describing it in terms of logic gates and other digital components. This is very different from programming in a language like C++ or Java, which are used to write software that runs on a regular computer.
Altera has its own flavor of HDL called Verilog, which is used specifically to program their FPGA chips. Verilog is a language that allows you to describe the behavior of digital circuits in a way that the FPGA can understand. You might use Verilog to tell the FPGA how to take in data from a sensor, process it, and output a result.
Overall, Altera's HDL is an important tool for electronics engineers and others who work with FPGA chips. By using HDL, you can create custom circuits that can be optimized for specific tasks, making them faster and more efficient than off-the-shelf solutions.