This is the 14802nd most frequent Russian word.
плотно
Tightly; densely.
Here, 'плотно' refers to the close arrangement or density of the furniture.
Мебель стоит так плотно, что пройти сложно.
The furniture is so tightly packed that it is hard to pass through.
In this context, 'плотно' characterizes the schedule as being compact and busy, indicating a lack of free time.
Он работает с плотным графиком, без перерывов.
He works with a tight schedule, without breaks.
In this sentence, 'плотно' describes the manner of how the subject ate, indicating that the meal was fulfilling and complete.