An artichoke is the edible immature flower bud of a thistle species, eaten before the bud opens. The name reached English from Arabic by way of Italian and Spanish.
Where the word came from
The chain runs from Arabic al-kharshuf through Andalusian Spanish alcarchofa into northern Italian articiocco, and from there into sixteenth century English. English speakers then reshaped the unfamiliar ending into choke, which is folk etymology rather than translation.
That accident of spelling produced a useful coincidence, because the inedible fibrous centre of the bud is genuinely called the choke.
What you are eating
An artichoke is a flower that has not opened. The fleshy bases of the bracts and the heart beneath them are the edible parts. The choke, the mass of fine hairs sitting on the heart, is the immature flower and is removed. If the bud is left on the plant it opens into a large purple thistle flower.
The symbolic sense
Because the edible part sits under many layers of protective bracts, the artichoke is a standing metaphor for something whose value has to be worked toward. It appears that way in cookery writing and in ordinary speech, as in peeling back the layers. In Renaissance Italy it also carried associations with wealth, since cultivating it was labour intensive.
Choosing and storing them
A good artichoke feels heavy for its size and the bracts squeak faintly when squeezed, which tells you the bud is still tightly closed and full of moisture. Bracts that have begun to splay outward mean the bud is maturing toward flower and the heart underneath will be tougher.
Cut surfaces oxidise within minutes, which is why recipes call for lemon water. Whole heads keep about a week refrigerated in a loose bag. The stem is edible and tastes much like the heart once the fibrous outer layer is peeled, so trimming it flush throws away one of the better parts.