Rope drop is inside the park at opening time, they will let you thru the turnstiles and then at certain points in the park they have ropes across and you can't go any further. Then at opening time/Rope drop they release the rope and you can go on the rides.
Also at most of the parks before rope drop the characters come out and do a little song/dance and there is a little 5 minute show to watch. We have never caught them before but plan on being there for rope drop each morning next month.
It's the park opening ceremony followed by the CMs literally dropping and removing the rope across the entrance to signify that the park is now open to the public. It's good fun and you get to see some of the characters some of them only show up for this and no where else, each park has some so watch out for them and see who you recognise.
I assume "rope drop" is at the advertised opening time of each park, and to witness this you would need to get there earlier to get through the turnstiles etc?