Step Parent Adoption

[Momwithquestions]

My question involves adoption law for the State of: TX

I have a six yr old, dad inst involved. We signed AOP at birth, no court orders for visitation or child support. Hubby wants to adopt, my son calls hubby daddy but is aware he is his step dad. Dad had been offered opportunity's to be involved in the past but messed them up, showing up drunk or just not showing up at all. He hasn't seen son since April, 06. I have asked dads permission to allow my husband to adopt dad says no, I understand that is his right. Dad had no job and is over 30, dad has been in jail many times for petty things like possession of prescription pills without a prescription, public intoxication etc. Was wondering about abandonment, and seeking a legal definition to Extreme Parental Disinterest. Been all over the web and cant even find it in the online law dictionary. Is it even a real legal term or something some parent made up??Thanks to all...