This is the 524th most frequent Spanish word.
iba
"Iba" is the imperfect tense of "ir," meaning "was going" or "used to go."
The word 'iba' here is the first-person singular imperfect tense of the verb 'ir', denoting a habitual action in the past.
Iba a la tienda todos los días cuando era niño.
I used to go to the store every day when I was a child.
In this sentence, 'iba' is used as the first-person singular imperfect tense of 'ir' to construct a periphrastic future tense in the past.
No sabía que iba a llover hoy.
I didn't know it was going to rain today.
Here, 'iba' is the third-person singular imperfect tense of 'ir', describing a continuing action in the past.