Are two waves out of phase only when the phase difference is $pi$?

Question

Excerpt from the Feynman Lectures, Volume III, Quantum Behavior:

At those places where the two waves arrive at the detector with a phase difference of $pi$ (where they are “out of phase”) the resulting wave motion at the detector will be the difference of the two amplitudes. The waves “interfere destructively,” and we get a low value for the wave intensity.

I watched Crash Course Physics #17 to visually understood what it means for two waves to "interfere destructively". That was lovely. But Feynman suggests that the out of phase condition is reached only when the phase difference is $pi$, specifically. Why is that?

Paul Razvan Berg · Accepted Answer

Although the idea can be interpreted as such, Feynman does not say that two waves are out of phase only when the phase difference is $pi$ (remember that $pi$ is a unit of radians, in degrees the equivalent value is 180°).
More generally, as per Wikipedia:

The difference $varphi(t) = phi_G(t) - phi_F(t)$ between the between the phases of two periodic signals $F$ and $G$ is called the phase difference of $G$ relative to $F$. At values of $t$ when the difference is zero, the two signals are said to be in phase, otherwise they are out of phase with each other.

Therefore, two waves are "out of phase" when the phase difference is non-zero.
An illustration:

Whit3rd · Answer

It is usual for a 'wave' to be modeled as a sine wave of a single
frequency (and wavelength).   While incoherent light is 'out of phase'
with such a wave, being entirely random, a collision  of two same-wavelength
waves is NOT incoherent,  and is said to be constructive interference
where the squared-amplitude of the sum is greater than the
sum of the squared-amplitudes of the waves.
This means the interference is constructive wherever phase difference is
in the range of (- π/2, + π/2) and destructive where phase difference
is in the range of (+ π/2, + 3 π/2).   When considering interference
fringes, the center of each 'fringe' which is a destructive-interference
zone, is at a phase difference of π.   That fringe center is the
minimum, but the entire zone is, to a lesser extent, destructive interference.
Of course, any integer times 2π can be arbitrarily added to the
phase, without changing the result, so there may be many zones of
interference.

Are two waves out of phase only when the phase difference is $pi$?

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