Here's a little exerpt from the booklet "Church Planting Movements" produced by the Int'l Missions Board of the Southern Baptist Church. You can read the entire booklet
here.

Planting "frog" rather than "lizard" churches.

Yes, this is a metaphor. Frog churches perceive themselves as ends in themselves, sitting fat and complacent on a hill or lily pad (or main street), expecting the lost to come to them in search of salvation. Frog churches hold meetings in places where they feel comfortable and require the lost to adapt to their froggy world. Lizard churches are always pursuing the lost. Adaptable and ready for action, they move quickly into the world through cracks and crevices seeking the lost. Lizard churches penetrate the homes of the lost with evangelistic Bible studies rather than requiring the lost to come to their churches. They are willing to change their colors, expend enormous energy, even lose their tails if necessary in order to bring the lost into the family of God.