Does Y mean latitude and X mean longitude in every GIS software?

For ESRI its almost always going to be:

Lat = Y Long = X

It's easy to get backwards. I've been doing this for years but still need to think about it sometimes.

On a standard north facing map, latitude is represented by horizontal lines, which go up and down (North and South) the Y axis. Its easy to think that since they are horizontal lines, they would be on the x axis, but they are not.

So similarly, the X axis is Longitude, as the values shift left to right (East and West) along the X axis. Confusing for the same reason since on a north facing map, these lines are vertical.

I'm mildly dyslexic so I always need to pause and think about it for a brief second when displaying new x/y data. Hope this helps.

No, for example when talking to a GeoServer WFS (or any other compliant WFS) the axis order depends on if you ask for version 1.0 or 1.1 of the spec in EPSG:4326.

X and Y are variables that can change for different purposes. For example: You may want to know the wind-speed, and you could use a sailboat's speed to know how fast is the wind going, so we can say: the sailboat = X and wind = Y. But it could also be that, you don't know how fast is the boat going and you can find its speed by knowing the wind-speed so now wind = X and sailboat = Y. However: The Equator, Prime meridian (at Greenwich), North and South, and Latitude and Longitude don't change. From the Equator to the North pole we measure Latitude 0° to 90° respectively, from the Equator to the South pole we measure 0° to -90° respectively. From the prime meridian at 0° we measure West up to -180° and East up to 180°. Sometimes -+ are replaced with West and East so that: -81° and 81°W mean the same thing. ESRI corporation regularly use X as longitude and Y as latitude.