Tech I, or "Technology I" is the first of three technology tiers currently in EVE. Tech I items are easier to fit and requires less skills than Tech II or III, but are weaker.
Generally speaking, Tech I equipment is the cheapest and most basic of the equipment available, but it also tends to encompass "named equipment" as well as the basic Tech I item. This named equipment is better than the basic Tech I item, but is not as good as Tech II gear. The named equipment does not need the additional skills that Tech II gear requires, however. Sometimes, the best named item is as good as Tech II, and in some cases can be better since they often have lower fitting requirements. Note that this is the usual, not in all cases.
The basic Tech I item does not have a Meta number, but it can be considered as "0". The named items have a Meta number from 1-4, with the higher numbered item being better than a lower numbered. With most weapons, if they are meta 4 It will have the same stats as their tech2 counterparts, apart from lower fitting requirements, the lack of a damage bonus from t2 weapon skills, and the inability to use TechII ammunition. Because of this, they are usually expensive to purchase on the markets.