First, when an attorney makes an objection during trial, it means that he does not like the way a question was asked. Or, he might believe that the question was phrased improperly.
When the attorney believes that there is no foundation upon which to ask a question he will often argue that the attorney has not asked baseline questions first before asking a key question.
Let me give you an example.
Let's say the case involves the claim that the doctor operated on the wrong side of the patient's brain. I could, theoretically simply ask the doctor “Isn't it true you operated on the wrong side of the brain?”
“Objection. No foundation.”
In that instance, I could ask the following series of questions:
“Doctor, isn't it true Mrs. Jones was a patient of yours?”
“You were treating her for many years, correct?”
"You diagnosed a benign tumor in her brain, correct?”
“You determined that she had this growth in her head that need to be removed.”
“You decided on January 1, 2013 you would perform surgery on her, true?”
"On January 1, 2013 you actually performed surgery on Mrs. Jones, correct?”
“Your intention was to operate on the right side of the brain to remove this benign tumor, correct?”
“Instead, during the surgery you operated on the left side of the brain, correct?”
“You would agree this patient had actually no problem and no medical condition on the left side of her brain, correct?”
“You would also agree that it would be a departure from good and accepted medical care to operate on a patient on a part of their body which did not need it, correct?”
Those questions simply establish a baseline for the jury to understand the steps leading up to the fateful surgery.
There are instances where the judge will permit me to ask a question even though there is no foundation. In some cases, I may ask the key question and then double back after I get the answer in order to lay a foundation. This way the jury will see the sequence of events that occurred leading up to the improper event.