alignment is the arrangement of things into a straight line or into correct position relative to one another — and, by extension, the state of agreement or association between people, groups, or goals.
The literal sense is mechanical and spatial. Wheels are out of alignment when their angles deviate from specification; type is set in alignment when its baselines agree; a surveyor's alignment is the ground plan of a road or railway, the line it takes across terrain before any grading is done. What all of these share is a reference line that is external to the parts being arranged. Alignment is never a property of one object alone — it is always a relation to something else, which is what separates it from straightness or order.
The figurative senses inherit that structure. In politics the word acquired its modern use in the 1930s, most visibly in the non-alignment of states declining to attach themselves to either Cold War bloc. In organizations, aligning incentives means arranging the rewards facing each party so that pursuing their own interest advances a shared aim. In artificial intelligence, alignment names the problem of making a system's behavior conform to the intentions and values of the people it acts for — the reference line being human intent rather than a machined tolerance.
The noun entered English in 1790 from French alignement, from aligner, "to arrange in a line," built from à and ligne, ultimately from Latin linea, "line." The -g- is unetymological, imported with the French spelling; the older English variant alinement survived in American usage well into the twentieth century.