What is "lagDiff" on MATLAB to evaluate the time difference from the cross-correlation ?

This is the sample program from MATLAB Documentation for xcorr and I'm troubled with understanding what lagDiff means on it.

I've checked the page which explains lag function on MATLAB, but still it is difficult to understand the meaning of "one time step".

load sensorData

t1 = (0:length(s1)-1)/Fs;
t2 = (0:length(s2)-1)/Fs;

subplot(2,1,1)
plot(t1,s1)
title('s_1')

subplot(2,1,2)
plot(t2,s2)
title('s_2')
xlabel('Time (s)')

[acor,lag] = xcorr(s2,s1);

[~,I] = max(abs(acor));
lagDiff = lag(I)
timeDiff = lagDiff/Fs

figure
plot(lag,acor)
a3 = gca;
a3.XTick = sort([-3000:1000:3000 lagDiff]);