Meaning of negative frequencies in Baseband non sinusoidal, non periodic signal
It means the same thing.
The negative frequencies are there to cancel out the complex portion of the signal in the time domain, so that the time domain signal is constrained to the real axis.
The Fourier Transform decomposes a signal, $x(t)$ onto a set of complex basis functions: $e^{-j\omega t}$ for $\omega \in (-\infty, \infty)$.
If $x(t)$ is real, then the decomposition, i.e. the Fourier Transform $X(\omega)$, must be such that the complex portions cancel out, when the inverse transform is performed to recompose the signal from it's constituent parts.
This is a conceptual explanation of why the Fourier Transform of a real signal is symmetric about $0$ Hz.