Definition of a Linear Time-Invariant (LTI) System
A linear time-invariant (LTI) system is a type of system in which the output is a linear combination of the input and its past values, and the system's characteristics do not change over time. In other words, the system's response to an input signal is the same regardless of when the input is applied.

Stability of an LTI System
The stability of an LTI system is an important property that determines whether the system can provide a well-behaved and predictable output. A stable system is one that produces a bounded output when excited by a bounded input, or when there is no input at all.

Option A: System Excited by Bounded Input, Output is Bounded
If a system is stable, it means that when it is excited by a bounded input signal (i.e., an input signal that does not exceed a certain limit), the output of the system should also remain bounded within a certain limit. This is because a stable system has the ability to control and limit the magnitude of the output signal, preventing it from growing indefinitely.

Option B: In the Absence of Input, Output Tends to Zero
Another way to assess the stability of an LTI system is by observing its behavior in the absence of an input signal. A stable system should have an output that tends to zero when there is no input. This means that even without any external input, the system should naturally settle to a state where the output is negligible or zero.

Option C: Both Option A and Option B
Option C states that a stable LTI system satisfies both the conditions mentioned in Option A and Option B. This implies that if a system is stable, it will produce a bounded output when excited by a bounded input, and its output will tend to zero in the absence of any input signal.

Conclusion
To summarize, a linear time-invariant (LTI) system is considered stable if it satisfies both conditions mentioned in Option A and Option B. This means that the system should produce a bounded output when excited by a bounded input, and its output should tend to zero when there is no input. These stability criteria are essential to ensure that the system behaves predictably and does not exhibit uncontrolled or erratic behavior.