Scanner:
The scanner, also known as the lexical analyzer, is a part of the compiler that analyzes the stream of characters from the input source code and breaks it down into a stream of words or tokens. It scans the characters one by one and groups them into meaningful units called lexemes.

Tokenization:
Tokenization is the process of dividing a sequence of characters into meaningful units, which are called tokens. These tokens represent the smallest meaningful units of the source code, such as keywords, identifiers, operators, literals, and punctuation symbols. The scanner performs tokenization by recognizing the patterns in the characters and categorizing them into different token types.

Word Stream:
The scanner produces a stream of words or tokens as its output. Each word or token is associated with its corresponding syntactic category, which provides information about its role in the source code. For example, keywords like "if" or "while" belong to the category of control statements, identifiers represent variable or function names, literals represent constant values, and so on.

Syntactic Categories:
Syntactic categories, also known as part-of-speech categories, are used to classify the words or tokens based on their grammatical roles in the source code. These categories provide information about the syntax or structure of the program. Some common syntactic categories include keywords, identifiers, operators, delimiters, literals, and comments.

Other Compiler Components:
- Optimizer: The optimizer is responsible for analyzing and transforming the intermediate representation of the source code to improve its efficiency. It performs various optimizations, such as eliminating redundant code, reducing memory usage, and improving execution speed.
- Parser: The parser is the component of the compiler that analyzes the stream of tokens produced by the scanner and checks if it conforms to the grammar rules of the programming language. It builds a parse tree or an abstract syntax tree (AST) that represents the structure of the source code.
- Code Generator: The code generator is responsible for translating the intermediate representation of the source code, such as the parse tree or AST, into machine code or bytecode that can be executed by the target hardware or virtual machine.

Conclusion:
In this question, the scanner is the part of the compiler that takes as input a stream of characters and produces as output a stream of words along with their associated syntactic categories. It performs tokenization and categorizes the characters into meaningful units, which are then used by other components of the compiler, such as the parser, optimizer, and code generator, to further process and analyze the source code.