Gaps: stock trading at $51 ask or bid being 50.95 a gap between the bid and ask. However, when stocks jump up or down proper filling its often called a gap. Stock closes at $35 and opens at $38. There is now a gap that must (at some time) need to be filled. In our case today there were big spreads between the bid and ask when we drop down to $46.15 (large spreads). These too at times must be filled, however its not always the case.