Write once, run anywhere (WORA), or sometimes Write once, run everywhere (WORE), was a 1995[1] slogan created by Sun Microsystems to illustrate the cross-platform benefits of the Java language.
[2][3] Ideally, this meant that a Java program could be developed on any device, compiled into standard bytecode, and be expected to run on any device equipped with a Java virtual machine (JVM).
The installation of a JVM or Java interpreter on chips, devices, or software packages became an industry standard practice.
The catch is that since there are multiple JVM implementations, on top of a wide variety of different operating systems, there could be subtle differences in how a program executes on each JVM/OS combination, possibly requiring an application to be tested on each target platform.
This gave rise to a joke among Java developers: Write Once, Debug Everywhere.