echo = true: Echo the code in the output document. If false the source code will be hidden.
results = "markup": The output format of the printed results. "markup" for literal block, "hidden" for hidden results, or anything else for raw output (I tend to use "tex" for Latex and "rst" for rest). Raw output is useful if you want to e.g. create tables from code chunks.
term = false: If true the output emulates a REPL session. Otherwise only stdout and figures will be included in output.
wrap = true: Wrap long lines from output.
line_width = 75: Line width for wrapped lines.
hold = false: Hold all results until the end of the chunk.
You can set the default chunk options (and weave arguments) for a document using weave_options key in YAML Header Configuration. E.g. to set the default out_width of all figures you can use:
---
weave_options:
out_width : 50%
----
You can also set or change the default chunk options for a document either before weave using the set_chunk_defaults function.