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A prefix-free code is a code in which no codeword appears as the initial segment (prefix) of any other codeword. For every pair of distinct codewords, neither may begin with the other as a prefix.

Conditions: Defined relative to concatenation of binary strings.; For every pair of distinct codewords $c_a$, $c_b$, neither $c_a$ is a prefix of $c_b$ nor $c_b$ is a prefix of $c_a$.

A prefix-free code is a code in which no codeword appears as the initial segment (prefix) of any other codeword. For every pair of distinct codewords, neither may begin with the other as a prefix.

Conditions: Defined relative to concatenation of binary strings.; For every pair of distinct codewords $c_a$, $c_b$, neither $c_a$ is a prefix of $c_b$ nor $c_b$ is a prefix of $c_a$.

An optimal code is defined as a code that is both instantaneous and has the minimum length measure L for the given source. The slide identifies Huffman codes as examples of optimum codes.

Conditions: Requires instantaneousness (prefix-freeness).; Requires minimum L for the given source, where L is not further defined in this clip.

An optimal code is defined as a code that is both instantaneous and has the minimum length measure L for the given source. The slide identifies Huffman codes as examples of optimum codes.

Conditions: Requires instantaneousness (prefix-freeness).; Requires minimum L for the given source, where L is not further defined in this clip.

A uniquely decodable code is a code where every encoded message sequence has only one valid decomposition into codewords. The video emphasizes that prefix-freeness guarantees this property, but the converse is not required; a code can be uniquely decodable without being prefix-free.

Conditions: Concerns decoding of concatenated codeword sequences at the receiver.; The video does not state a formal symbolic definition beyond the examples and prose.

A uniquely decodable code is a code where every encoded message sequence has only one valid decomposition into codewords. The video emphasizes that prefix-freeness guarantees this property, but the converse is not required; a code can be uniquely decodable without being prefix-free.

Conditions: Concerns decoding of concatenated codeword sequences at the receiver.; The video does not state a formal symbolic definition beyond the examples and prose.