Specialties
An entry on the skill list may represent an entire category of closely related skills that share a single skill name. Examples include Armoury and Survival. Skills like this are in Specialty Skills category. The skills within such a category are called "specialties." When you buy a general skill of this kind, you must specify which specialty you are learning. On your character sheet, note the name of the specialty in parentheses after the general skill name; e.g., "Armoury (Small Arms)" or "Survival (Arctic)."
You may learn skills like this any number of times, with a different specialty each time, because each specialty is a different skill. There is usually a favorable "default" between specialties (see Skill Defaults), which may let you purchase additional specialties more cheaply.
Optional Specialties
Many IQ-based skills – notably "academic" skills such as Literature and Physics – have countless subfields but do not require you to select a specialty. As written, if you learn a skill like this, you are a generalist, knowledgeable about every aspect of the skill. However, you may opt to specialize in a single, narrow area. You may only do this with an Average or harder IQ-based skill, and only if the GM agrees that the chosen subfield is logical given the skill and your TL.
When you choose an optional specialty, write down the skill and its specialty just as if you were selecting a required specialty. You learn the specialized skill as if it were one level easier. Unless otherwise noted, prerequisites are unchanged. The general skill defaults to the specialized one at -2; roll against this whenever you must answer questions outside your field. Any skill that defaults to the general skill also defaults to all of its optional specialties, but at an additional -2.
Example: Chemistry is IQ/Hard and does not require a specialty. You could learn the optional specialty Chemistry (Analytical) as if it were one level easier, or IQ/Average. Your general Chemistry skill would default to Chemistry (Analytical)-2. Metallurgy, which normally defaults to Chemistry-5, would default to Chemistry (Analytical)-7.