Reverence and love towards God,
and showing this love with obedience to His will, and devotion to
serving Him.

Piety is also, "Reverence of parents
or friends, accompanied with
affection and devotion to their
honor and happiness."  
(Webster's 1828)      
...But if any widow have children or nephews, let them learn first to show piety at home, and to requite their parents; for that is good and acceptable before God.

1 Timothy 5:4