Part of learning about signals and systems is that systems are identified according to certain properties they exhibit. Have a look at the core system classifications:
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Linearity: A linear combination of individually obtained outputs is equivalent to the output obtained by the system operating on the corresponding linear combination of inputs.
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Time-invariant: The system properties don't change with time. A present input produces the same response as it does in the future, less the time shift factor between the present and future.
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Memoryless: If the present system output depends only on the present input, the system is memoryless.
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Causal: The present system output depends at most on the present and past inputs. Future inputs can't be used to produce the present output.
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Stable: A system is bounded-input bound-output (BIBO) stable if all bounded inputs produce a bounded output.
This table presents core linear time invariant (LTI) system properties for both continuous and discrete-time systems. Time-domain, frequency-domain, and s/z-domain properties are identified for the categories basic input/output, cascading, linear constant coefficient (LCC) differential and difference equations, and BIBO stability:
