Definition of "boulder"

There were four sizes of marbles and we called them boulders, biggies, regulars, and teenies.

2006, Carol Benson, The Old Lonesome, page 84

He bouldered a route in the same area with ease. Mitchell, 11, was hanging with the older kids in an area where bouldering nearly upside down seemed to be....

2005 November 18, “The ties that bind ..., ... and prevent falls have become family unifier in rock climbing”, in Salt Lake Tribune

As the week unfolded, we were taught about the equipment we needed, how to tie a rope and what to wear. We learnt to balance on our feet rather than cling on with our arms and to trust our rock shoes, the moulded rubber slippers that can grip the smoothest of surfaces. We abseiled, bouldered and belayed.

2006 July 18, Tony Durrant, “The steep learning curve”, in telegraph.co.uk

There's even old climbing hardware in it because people bouldered on it for years.

2007 February 15, “Homes blend eco-friendliness, unique design”, in Sierra Sun