Intelligent weapons have an Ego score
My copy of the PHB does not have an index listing for Ego Weapon, but my DMG has an index listing for
Ego, of intelligent weapons
Thus I have to wonder whether what you are reading as "Ego Weapons" is meant to be written as "Ego, weapons".
As far as I know, there is no such thing as an Ego weapon per se. Rather, there are Intelligent Weapons, and all Intelligent Weapons will have an Ego score. The Ego score is based on the number and power of the special abilities of the weapon. Weapons that have a high enough Personality (Intelligence + Ego) can dominate the characters that try to use them.
2e DMG (Appendix 3, Section 'Intelligent Weapons', Subsection 'Weapon Ego')
Only after all aspects of a weapon have been determined and recorded can the ego rating of a weapon be found. Ego, along with intelligence, will be a factor with regard to the dominance of weapon over character, as detailed on table 119.
Although the calculation of the Ego score differs, this is essentially the same concept as was found in both first edition and the Expert rules of BECMI. According to Daniel R. Collins, the concept goes back to OD&D.