These are all the holidays (sabbats) in the Wheel of the Year. Instead of breaking the 12 months into four seasons of uneven length based on the calendar it instead breaks the year into 8 approximate 6-week intervals that are based on the solaces and equinoxes. So Lughnasadh occurred on August 1 which means we have hit the middle point between the summer solstice and the autumn equinox. So we are in the fall half of summer. Once we hit the autumn equinox (Mabon) we have 6 weeks of fall, before we hit Samhain on Halloween where we move to the winter part of fall. Its a much better way to think about seasons

You can look up the dates online or read the wonderful series on Sabbats by Llewellyn