Android devices have CPUs. Many of those CPUs are based on the ARM architecture, while some are based on x86, and a few others are based on other stuff like MIPS.
Some Android apps use the Native Development Kit (NDK) to create C/C++ code to link into their app. C/C++ code needs to be compiled for a specific CPU architecture. The NDK places the version of the C/C++ code compiled for each architecture into an architecture-specific directory. One of those directories is armeabi/, which is for a generic ARM CPU. There is also armeabi-v7/ (for an ARM v7-compatible CPU), x86/ (for x86 CPUs), etc.